Redesign doc service UX for scale + add group-based document sharing

- Three-column layout: Sidebar + SourcePanel (views + searchable category tree) + main
- DocumentSlideOver (480px right panel): inline editing, type picker, AI suggestion confirm/reject,
  categories combobox, tags editor, sharing section, raw text, re-analyse/delete actions
- ManageCategoriesDialog: inline rename, delete with confirm, search filter
- DocumentsPage rewrite: filter chip system, multi-file upload queue, drag-and-drop overlay,
  bulk actions bar (share/delete), smart TanStack Query polling, URL-driven view state
- Sidebar simplified: per-category NavLinks removed; Documents = single NavLink under Apps
- Backend: document_shares table (migration 0004), share CRUD endpoints, shared-with-me view,
  N+1-safe share_count via GROUP BY, recipient download access, X-User-Groups header enforcement
- Gateway proxy: injects X-User-Groups header into all document + category proxy requests
- Backend users: GET /api/users/me/groups endpoint for share picker combobox
- CLAUDE.md, STATUS.md files, and changelog updated

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/schemas/user.py

@@ -1,4 +1,5 @@
 import re
+from datetime import datetime
 
 from pydantic import BaseModel, EmailStr, Field, field_validator
 
@@ -116,6 +117,15 @@ class ColorModeUpdate(BaseModel):
         return v
 
 
+class UserGroupOut(BaseModel):
+    """A group the current user belongs to — used for the share picker."""
+    id: str
+    name: str
+    description: str | None
+
+    model_config = {"from_attributes": True}
+
+
 class DashboardPrefsUpdate(BaseModel):
     app_ids: list[str] = Field(default_factory=list)