Redesign teams portal and add user autocomplete for member invitations

- Redesign TeamsPage with modern card-based layout including stats bar,
  search functionality, and empty states
- Add UserAutocomplete component with debounced search and keyboard
  navigation for selecting existing users
- Add /api/v1/users/search endpoint for username prefix search
- Update TeamMembersPage to use UserAutocomplete instead of free text input

backend/app/routes.py

@@ -1093,6 +1093,43 @@ def oidc_callback(
     return response
 
 
+# --- User Search Routes (for autocomplete) ---
+
+
+@router.get("/api/v1/users/search")
+def search_users(
+    q: str = Query(..., min_length=1, description="Search query for username"),
+    limit: int = Query(default=10, ge=1, le=50, description="Maximum results"),
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """
+    Search for users by username prefix.
+    Returns basic user info for autocomplete (no email for privacy).
+    Any authenticated user can search.
+    """
+    search_pattern = f"{q.lower()}%"
+    users = (
+        db.query(User)
+        .filter(
+            func.lower(User.username).like(search_pattern),
+            User.is_active == True,
+        )
+        .order_by(User.username)
+        .limit(limit)
+        .all()
+    )
+
+    return [
+        {
+            "id": str(u.id),
+            "username": u.username,
+            "is_admin": u.is_admin,
+        }
+        for u in users
+    ]
+
+
 # --- Admin User Management Routes ---