Add comprehensive backend features and mobile UI improvements

Backend:
- Add 2FA authentication with TOTP support
- Add API keys management system
- Add audit logging for security events
- Add file upload/management system
- Add notifications system with preferences
- Add session management
- Add webhooks integration
- Add analytics endpoints
- Add export functionality
- Add password policy enforcement
- Add new database migrations for core tables

Frontend:
- Add module position system (top/bottom sidebar sections)
- Add search and notifications module configuration tabs
- Add mobile logo replacing hamburger menu
- Center page title absolutely when no tabs present
- Align sidebar footer toggles with navigation items
- Add lighter icon color in dark theme for mobile
- Add API keys management page
- Add notifications page with context
- Add admin analytics and audit logs pages

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

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

backend/app/schemas/notification.py

@@ -0,0 +1,75 @@
+"""Pydantic schemas for Notification API requests/responses."""
+
+from datetime import datetime
+from typing import Optional, List, Any
+from pydantic import BaseModel, Field
+
+
+class NotificationBase(BaseModel):
+    """Base notification schema."""
+    title: str = Field(..., min_length=1, max_length=200)
+    message: Optional[str] = None
+    type: str = Field(default="info", pattern="^(info|success|warning|error|system)$")
+    link: Optional[str] = Field(None, max_length=500)
+    extra_data: Optional[dict] = None
+
+
+class NotificationCreate(NotificationBase):
+    """Schema for creating a notification."""
+    user_id: str  # Required for system/admin notifications
+
+
+class NotificationCreateForUser(NotificationBase):
+    """Schema for creating a notification for a specific user (admin use)."""
+    pass
+
+
+class Notification(BaseModel):
+    """Schema for notification response."""
+    id: str
+    user_id: str
+    title: str
+    message: Optional[str] = None
+    type: str
+    link: Optional[str] = None
+    extra_data: Optional[dict] = None
+    is_read: bool
+    created_at: datetime
+    read_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class NotificationList(BaseModel):
+    """Schema for paginated notification list."""
+    items: List[Notification]
+    total: int
+    unread_count: int
+
+
+class NotificationStats(BaseModel):
+    """Schema for notification statistics."""
+    total: int
+    unread: int
+    by_type: dict[str, int]
+
+
+class NotificationBulkAction(BaseModel):
+    """Schema for bulk notification actions."""
+    notification_ids: List[str]
+
+
+class NotificationPreferences(BaseModel):
+    """Schema for user notification preferences."""
+    email_notifications: bool = True
+    push_notifications: bool = True
+    notification_types: dict[str, bool] = Field(
+        default_factory=lambda: {
+            "info": True,
+            "success": True,
+            "warning": True,
+            "error": True,
+            "system": True
+        }
+    )