feat(rag): RAG scoping and context isolation controls

- Migration 0030: add conversations.rag_project_id (NULL=orphan-only,
  -1=all notes, positive=project), projects.auto_summary and
  projects.summary_updated_at
- Three-value scope semantics thread from build_context() → semantic
  search and keyword fallback via orphan_only + effective_project_id
- Project summarization background job (generate_project_summary,
  backfill_project_summaries) called via Ollama; triggered on project
  update and note saves (debounced 1h); runs at startup
- New LLM tools: search_projects (SequenceMatcher scoring on
  title+description+auto_summary) and set_rag_scope (persists to DB,
  workspace-guarded, emits new_rag_scope in SSE done event)
- execute_tool() accepts conv_id + workspace_project_id; generation_task
  passes both and captures scope changes for SSE done enrichment
- Frontend: Conversation type gets rag_project_id; chat store adds
  ragProjectId computed + updateRagScope(); SSE done handler syncs scope
- ChatView: replace sidebar ProjectSelector with a scope chip pill above
  the input bar, animated dropdown, pulse on model-driven scope change

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

src/fabledassistant/routes/chat.py

@@ -115,13 +115,15 @@ async def delete_conversation_route(conv_id: int):
 @chat_bp.route("/conversations/<int:conv_id>", methods=["PATCH"])
 @login_required
 async def update_conversation_route(conv_id: int):
+    from fabledassistant.services.chat import _UNSET
     uid = get_current_user_id()
     data = await request.get_json()
     title = data.get("title")
     model = data.get("model")
-    if title is None and model is None:
-        return jsonify({"error": "title or model is required"}), 400
-    conv = await update_conversation(uid, conv_id, title=title, model=model)
+    rag_project_id = data.get("rag_project_id", _UNSET)
+    if title is None and model is None and rag_project_id is _UNSET:
+        return jsonify({"error": "title, model, or rag_project_id is required"}), 400
+    conv = await update_conversation(uid, conv_id, title=title, model=model, rag_project_id=rag_project_id)
     if conv is None:
         return not_found("Conversation")
     return jsonify(conv.to_dict())