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/migrations/versions/011_custom_fields_tables.py

@@ -0,0 +1,70 @@
+"""Add custom fields and task custom values tables
+
+Revision ID: 011
+Revises: 010
+Create Date: 2026-01-05
+
+FEAT-001: Add custom fields feature for flexible task data extension.
+"""
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = '011'
+down_revision: Union[str, None] = '010'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # Create field_type_enum
+    field_type_enum = sa.Enum(
+        'text', 'number', 'dropdown', 'date', 'person', 'formula',
+        name='field_type_enum'
+    )
+    field_type_enum.create(op.get_bind(), checkfirst=True)
+
+    # Create pjctrl_custom_fields table
+    op.create_table(
+        'pjctrl_custom_fields',
+        sa.Column('id', sa.String(36), primary_key=True),
+        sa.Column('project_id', sa.String(36), sa.ForeignKey('pjctrl_projects.id', ondelete='CASCADE'), nullable=False),
+        sa.Column('name', sa.String(100), nullable=False),
+        sa.Column('field_type', field_type_enum, nullable=False),
+        sa.Column('options', sa.JSON, nullable=True),
+        sa.Column('formula', sa.Text, nullable=True),
+        sa.Column('is_required', sa.Boolean, default=False, nullable=False),
+        sa.Column('position', sa.Integer, default=0, nullable=False),
+        sa.Column('created_at', sa.DateTime, server_default=sa.func.now(), nullable=False),
+        sa.Column('updated_at', sa.DateTime, server_default=sa.func.now(), onupdate=sa.func.now(), nullable=False),
+    )
+
+    # Create indexes for custom_fields
+    op.create_index('ix_pjctrl_custom_fields_project_id', 'pjctrl_custom_fields', ['project_id'])
+
+    # Create pjctrl_task_custom_values table
+    op.create_table(
+        'pjctrl_task_custom_values',
+        sa.Column('id', sa.String(36), primary_key=True),
+        sa.Column('task_id', sa.String(36), sa.ForeignKey('pjctrl_tasks.id', ondelete='CASCADE'), nullable=False),
+        sa.Column('field_id', sa.String(36), sa.ForeignKey('pjctrl_custom_fields.id', ondelete='CASCADE'), nullable=False),
+        sa.Column('value', sa.Text, nullable=True),
+        sa.Column('updated_at', sa.DateTime, server_default=sa.func.now(), onupdate=sa.func.now(), nullable=False),
+        sa.UniqueConstraint('task_id', 'field_id', name='uq_task_field'),
+    )
+
+    # Create indexes for task_custom_values
+    op.create_index('ix_pjctrl_task_custom_values_task_id', 'pjctrl_task_custom_values', ['task_id'])
+    op.create_index('ix_pjctrl_task_custom_values_field_id', 'pjctrl_task_custom_values', ['field_id'])
+
+
+def downgrade() -> None:
+    op.drop_index('ix_pjctrl_task_custom_values_field_id', table_name='pjctrl_task_custom_values')
+    op.drop_index('ix_pjctrl_task_custom_values_task_id', table_name='pjctrl_task_custom_values')
+    op.drop_table('pjctrl_task_custom_values')
+
+    op.drop_index('ix_pjctrl_custom_fields_project_id', table_name='pjctrl_custom_fields')
+    op.drop_table('pjctrl_custom_fields')
+
+    # Drop the enum type
+    sa.Enum(name='field_type_enum').drop(op.get_bind(), checkfirst=True)