Add multi-user auth, background generation, and chat UX improvements

Phase 5: Multi-user authentication with session cookies, bcrypt passwords,
first-user-is-admin pattern, per-user data isolation, backup/restore,
Docker Swarm production stack with secrets and network isolation.

Phase 5.1: Chat UX improvements:
- Background generation architecture (GenerationBuffer + asyncio task)
  with SSE fan-out, reconnect support, and periodic DB flushes
- LLM-generated conversation titles (first exchange + every 10th message)
- Stop generation button with cancel_event and partial content preservation
- Relative timestamps in sidebar (5m ago, 3h ago, then dates)
- Empty chat auto-cleanup on navigation away
- Save-as-note uses LLM for title generation, tags notes with "chat"
- Summarize-as-note also tags with "chat"

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

src/fabledassistant/routes/settings.py

@@ -1,5 +1,6 @@
 from quart import Blueprint, jsonify, request
 
+from fabledassistant.auth import login_required, get_current_user_id
 from fabledassistant.services.llm import get_installed_models
 from fabledassistant.services.settings import get_all_settings, set_settings_batch
 
@@ -7,13 +8,17 @@ settings_bp = Blueprint("settings", __name__, url_prefix="/api/settings")
 
 
 @settings_bp.route("", methods=["GET"])
+@login_required
 async def get_settings_route():
-    settings = await get_all_settings()
+    uid = get_current_user_id()
+    settings = await get_all_settings(uid)
     return jsonify(settings)
 
 
 @settings_bp.route("", methods=["PUT"])
+@login_required
 async def update_settings_route():
+    uid = get_current_user_id()
     data = await request.get_json()
     if not isinstance(data, dict):
         return jsonify({"error": "Expected a JSON object"}), 400
@@ -24,6 +29,6 @@ async def update_settings_route():
         if installed and model not in installed:
             return jsonify({"error": f"Model '{model}' is not installed"}), 400
 
-    await set_settings_batch({k: str(v) for k, v in data.items()})
-    settings = await get_all_settings()
+    await set_settings_batch(uid, {k: str(v) for k, v in data.items()})
+    settings = await get_all_settings(uid)
     return jsonify(settings)