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/session.py

@@ -0,0 +1,55 @@
+"""Pydantic schemas for User Session API requests/responses."""
+
+from datetime import datetime
+from typing import Optional, List
+from pydantic import BaseModel, Field
+
+
+class SessionBase(BaseModel):
+    """Base session schema."""
+    device_name: Optional[str] = Field(None, max_length=200)
+    device_type: Optional[str] = Field(None, max_length=50)
+    browser: Optional[str] = Field(None, max_length=100)
+    os: Optional[str] = Field(None, max_length=100)
+    ip_address: Optional[str] = Field(None, max_length=45)
+    location: Optional[str] = Field(None, max_length=200)
+
+
+class SessionCreate(SessionBase):
+    """Schema for creating a session."""
+    user_id: str
+    token_hash: str
+    user_agent: Optional[str] = None
+    expires_at: Optional[datetime] = None
+
+
+class Session(BaseModel):
+    """Schema for session response."""
+    id: str
+    user_id: str
+    device_name: Optional[str] = None
+    device_type: Optional[str] = None
+    browser: Optional[str] = None
+    os: Optional[str] = None
+    ip_address: Optional[str] = None
+    location: Optional[str] = None
+    is_active: bool
+    is_current: bool
+    created_at: datetime
+    last_active_at: Optional[datetime] = None
+    expires_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class SessionList(BaseModel):
+    """Schema for session list."""
+    items: List[Session]
+    total: int
+    active_count: int
+
+
+class SessionRevokeRequest(BaseModel):
+    """Schema for revoking sessions."""
+    session_ids: List[str]