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/file.py

@@ -0,0 +1,87 @@
+"""File storage schemas."""
+
+from datetime import datetime
+from typing import Optional, List
+from pydantic import BaseModel, Field
+
+
+class FileBase(BaseModel):
+    """Base file schema."""
+    description: Optional[str] = None
+    tags: Optional[List[str]] = None
+    is_public: bool = False
+
+
+class FileCreate(FileBase):
+    """Schema for file upload metadata."""
+    pass
+
+
+class FileUpdate(BaseModel):
+    """Schema for updating file metadata."""
+    description: Optional[str] = None
+    tags: Optional[List[str]] = None
+    is_public: Optional[bool] = None
+
+
+class StoredFile(FileBase):
+    """File response schema."""
+    id: str
+    original_filename: str
+    content_type: Optional[str] = None
+    size_bytes: int
+    storage_type: str
+    uploaded_by: Optional[str] = None
+    file_hash: Optional[str] = None
+    created_at: datetime
+    updated_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+class FileUploadResponse(BaseModel):
+    """Response after successful file upload."""
+    id: str
+    original_filename: str
+    content_type: Optional[str] = None
+    size_bytes: int
+    download_url: str
+
+
+class FileListResponse(BaseModel):
+    """Response for file listing."""
+    files: List[StoredFile]
+    total: int
+    page: int
+    page_size: int
+
+
+# Allowed file types for upload
+ALLOWED_CONTENT_TYPES = [
+    # Images
+    "image/jpeg",
+    "image/png",
+    "image/gif",
+    "image/webp",
+    "image/svg+xml",
+    # Documents
+    "application/pdf",
+    "application/msword",
+    "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
+    "application/vnd.ms-excel",
+    "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+    "text/plain",
+    "text/csv",
+    # Archives
+    "application/zip",
+    "application/x-tar",
+    "application/gzip",
+    # JSON/XML
+    "application/json",
+    "application/xml",
+    "text/xml",
+]
+
+# Maximum file size (10 MB by default)
+MAX_FILE_SIZE = 10 * 1024 * 1024