feat: add supporting data capture, PDF export, and branding settings UI

- API clients for supporting data CRUD and team branding
- AddSupportingDataModal with text snippet and screenshot tabs (paste + upload)
- SupportingDataPanel collapsible section integrated into both session runners
- ExportPreviewModal updated with PDF format and server-side download flow
- BrandingSettings component for company name and logo management
- Expose team_id in UserResponse schema for branding endpoint access

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/schemas/user.py

@@ -46,6 +46,7 @@ class UserResponse(UserBase):
     role: str = "engineer"
     account_id: Optional[UUID] = None
     account_role: Optional[str] = None
+    team_id: Optional[UUID] = None
     is_super_admin: bool = False
     is_active: bool = True
     must_change_password: bool = False