feat: implement custom fields, gantt view, calendar view, and file encryption

- Custom Fields (FEAT-001):
  - CustomField and TaskCustomValue models with formula support
  - CRUD API for custom field management
  - Formula engine for calculated fields
  - Frontend: CustomFieldEditor, CustomFieldInput, ProjectSettings page
  - Task list API now includes custom_values
  - KanbanBoard displays custom field values

- Gantt View (FEAT-003):
  - TaskDependency model with FS/SS/FF/SF dependency types
  - Dependency CRUD API with cycle detection
  - start_date field added to tasks
  - GanttChart component with Frappe Gantt integration
  - Dependency type selector in UI

- Calendar View (FEAT-004):
  - CalendarView component with FullCalendar integration
  - Date range filtering API for tasks
  - Drag-and-drop date updates
  - View mode switching in Tasks page

- File Encryption (FEAT-010):
  - AES-256-GCM encryption service
  - EncryptionKey model with key rotation support
  - Admin API for key management
  - Encrypted upload/download for confidential projects

- Migrations: 011 (custom fields), 012 (encryption keys), 013 (task dependencies)
- Updated issues.md with completion status

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/schemas/custom_field.py

@@ -0,0 +1,88 @@
+from pydantic import BaseModel, Field, field_validator
+from typing import Optional, List, Any, Dict
+from datetime import datetime
+from enum import Enum
+
+
+class FieldType(str, Enum):
+    TEXT = "text"
+    NUMBER = "number"
+    DROPDOWN = "dropdown"
+    DATE = "date"
+    PERSON = "person"
+    FORMULA = "formula"
+
+
+class CustomFieldBase(BaseModel):
+    name: str = Field(..., min_length=1, max_length=100)
+    field_type: FieldType
+    options: Optional[List[str]] = None  # For dropdown type
+    formula: Optional[str] = None  # For formula type
+    is_required: bool = False
+
+    @field_validator('options')
+    @classmethod
+    def validate_options(cls, v, info):
+        field_type = info.data.get('field_type')
+        if field_type == FieldType.DROPDOWN:
+            if not v or len(v) == 0:
+                raise ValueError('Dropdown fields must have at least one option')
+            if len(v) > 50:
+                raise ValueError('Dropdown fields can have at most 50 options')
+        return v
+
+    @field_validator('formula')
+    @classmethod
+    def validate_formula(cls, v, info):
+        field_type = info.data.get('field_type')
+        if field_type == FieldType.FORMULA and not v:
+            raise ValueError('Formula fields must have a formula expression')
+        return v
+
+
+class CustomFieldCreate(CustomFieldBase):
+    pass
+
+
+class CustomFieldUpdate(BaseModel):
+    name: Optional[str] = Field(None, min_length=1, max_length=100)
+    options: Optional[List[str]] = None
+    formula: Optional[str] = None
+    is_required: Optional[bool] = None
+
+
+class CustomFieldResponse(CustomFieldBase):
+    id: str
+    project_id: str
+    position: int
+    created_at: datetime
+    updated_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+class CustomFieldListResponse(BaseModel):
+    fields: List[CustomFieldResponse]
+    total: int
+
+
+# Task custom value schemas
+class CustomValueInput(BaseModel):
+    field_id: str
+    value: Optional[Any] = None  # Can be string, number, date string, or user id
+
+
+class CustomValueResponse(BaseModel):
+    field_id: str
+    field_name: str
+    field_type: FieldType
+    value: Optional[Any] = None
+    display_value: Optional[str] = None  # Formatted for display
+
+    class Config:
+        from_attributes = True
+
+
+class TaskCustomValuesUpdate(BaseModel):
+    custom_values: List[CustomValueInput]

backend/app/schemas/encryption_key.py

@@ -0,0 +1,46 @@
+"""Schemas for encryption key API."""
+from datetime import datetime
+from typing import List, Optional
+from pydantic import BaseModel
+
+
+class EncryptionKeyResponse(BaseModel):
+    """Response schema for encryption key (without actual key data)."""
+    id: str
+    algorithm: str
+    is_active: bool
+    created_at: datetime
+    rotated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class EncryptionKeyListResponse(BaseModel):
+    """Response schema for list of encryption keys."""
+    keys: List[EncryptionKeyResponse]
+    total: int
+
+
+class EncryptionKeyCreateResponse(BaseModel):
+    """Response schema after creating a new encryption key."""
+    id: str
+    algorithm: str
+    is_active: bool
+    created_at: datetime
+    message: str
+
+
+class EncryptionKeyRotateResponse(BaseModel):
+    """Response schema after key rotation."""
+    new_key_id: str
+    old_key_id: Optional[str]
+    message: str
+
+
+class EncryptionStatusResponse(BaseModel):
+    """Response schema for encryption status."""
+    encryption_available: bool
+    active_key_id: Optional[str]
+    total_keys: int
+    message: str

backend/app/schemas/task.py

@@ -1,5 +1,5 @@
 from pydantic import BaseModel
-from typing import Optional, List
+from typing import Optional, List, Any, Dict
 from datetime import datetime
 from decimal import Decimal
 from enum import Enum
@@ -12,11 +12,27 @@ class Priority(str, Enum):
     URGENT = "urgent"
 
 
+class CustomValueInput(BaseModel):
+    """Input for setting a custom field value."""
+    field_id: str
+    value: Optional[Any] = None  # Can be string, number, date string, or user id
+
+
+class CustomValueResponse(BaseModel):
+    """Response for a custom field value."""
+    field_id: str
+    field_name: str
+    field_type: str
+    value: Optional[Any] = None
+    display_value: Optional[str] = None  # Formatted for display
+
+
 class TaskBase(BaseModel):
     title: str
     description: Optional[str] = None
     priority: Priority = Priority.MEDIUM
     original_estimate: Optional[Decimal] = None
+    start_date: Optional[datetime] = None
     due_date: Optional[datetime] = None
 
 
@@ -24,6 +40,7 @@ class TaskCreate(TaskBase):
     parent_task_id: Optional[str] = None
     assignee_id: Optional[str] = None
     status_id: Optional[str] = None
+    custom_values: Optional[List[CustomValueInput]] = None
 
 
 class TaskUpdate(BaseModel):
@@ -32,8 +49,10 @@ class TaskUpdate(BaseModel):
     priority: Optional[Priority] = None
     original_estimate: Optional[Decimal] = None
     time_spent: Optional[Decimal] = None
+    start_date: Optional[datetime] = None
     due_date: Optional[datetime] = None
     position: Optional[int] = None
+    custom_values: Optional[List[CustomValueInput]] = None
 
 
 class TaskStatusUpdate(BaseModel):
@@ -67,6 +86,7 @@ class TaskWithDetails(TaskResponse):
     status_color: Optional[str] = None
     creator_name: Optional[str] = None
     subtask_count: int = 0
+    custom_values: Optional[List[CustomValueResponse]] = None
 
 
 class TaskListResponse(BaseModel):

backend/app/schemas/task_dependency.py

@@ -0,0 +1,78 @@
+from pydantic import BaseModel, field_validator
+from typing import Optional, List
+from datetime import datetime
+from enum import Enum
+
+
+class DependencyType(str, Enum):
+    """Task dependency types for Gantt chart."""
+    FS = "FS"  # Finish-to-Start (most common)
+    SS = "SS"  # Start-to-Start
+    FF = "FF"  # Finish-to-Finish
+    SF = "SF"  # Start-to-Finish (rare)
+
+
+class TaskDependencyCreate(BaseModel):
+    """Schema for creating a task dependency."""
+    predecessor_id: str
+    dependency_type: DependencyType = DependencyType.FS
+    lag_days: int = 0
+
+    @field_validator('lag_days')
+    @classmethod
+    def validate_lag_days(cls, v):
+        if v < -365 or v > 365:
+            raise ValueError('lag_days must be between -365 and 365')
+        return v
+
+
+class TaskDependencyUpdate(BaseModel):
+    """Schema for updating a task dependency."""
+    dependency_type: Optional[DependencyType] = None
+    lag_days: Optional[int] = None
+
+    @field_validator('lag_days')
+    @classmethod
+    def validate_lag_days(cls, v):
+        if v is not None and (v < -365 or v > 365):
+            raise ValueError('lag_days must be between -365 and 365')
+        return v
+
+
+class TaskInfo(BaseModel):
+    """Brief task information for dependency response."""
+    id: str
+    title: str
+    start_date: Optional[datetime] = None
+    due_date: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class TaskDependencyResponse(BaseModel):
+    """Schema for task dependency response."""
+    id: str
+    predecessor_id: str
+    successor_id: str
+    dependency_type: DependencyType
+    lag_days: int
+    created_at: datetime
+    predecessor: Optional[TaskInfo] = None
+    successor: Optional[TaskInfo] = None
+
+    class Config:
+        from_attributes = True
+
+
+class TaskDependencyListResponse(BaseModel):
+    """Schema for list of task dependencies."""
+    dependencies: List[TaskDependencyResponse]
+    total: int
+
+
+class DependencyValidationError(BaseModel):
+    """Schema for dependency validation error details."""
+    error_type: str  # 'circular', 'self_reference', 'duplicate', 'cross_project'
+    message: str
+    details: Optional[dict] = None