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/012_encryption_keys_table.py

@@ -0,0 +1,48 @@
+"""Encryption keys table and attachment encryption_key_id
+
+Revision ID: 012
+Revises: 011
+Create Date: 2026-01-05
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers
+revision = '012'
+down_revision = '011'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # Create encryption_keys table
+    op.create_table(
+        'pjctrl_encryption_keys',
+        sa.Column('id', sa.String(36), primary_key=True),
+        sa.Column('key_data', sa.Text, nullable=False),  # Encrypted key using Master Key
+        sa.Column('algorithm', sa.String(20), default='AES-256-GCM', nullable=False),
+        sa.Column('is_active', sa.Boolean, default=True, nullable=False),
+        sa.Column('created_at', sa.DateTime, server_default=sa.func.now(), nullable=False),
+        sa.Column('rotated_at', sa.DateTime, nullable=True),
+    )
+    op.create_index('idx_encryption_key_active', 'pjctrl_encryption_keys', ['is_active'])
+
+    # Add encryption_key_id column to attachments table
+    op.add_column(
+        'pjctrl_attachments',
+        sa.Column(
+            'encryption_key_id',
+            sa.String(36),
+            sa.ForeignKey('pjctrl_encryption_keys.id', ondelete='SET NULL'),
+            nullable=True
+        )
+    )
+    op.create_index('idx_attachment_encryption_key', 'pjctrl_attachments', ['encryption_key_id'])
+
+
+def downgrade():
+    op.drop_index('idx_attachment_encryption_key', 'pjctrl_attachments')
+    op.drop_column('pjctrl_attachments', 'encryption_key_id')
+    op.drop_index('idx_encryption_key_active', 'pjctrl_encryption_keys')
+    op.drop_table('pjctrl_encryption_keys')