Phase 21: Intent-first pipeline, visible ack, KV-stable system prompt

Pipeline changes (generation_task.py, intent.py):
- Remove optimistic streaming queue/race (_drain_queue deleted)
- Remove _generate_acknowledgment — ack now embedded in intent JSON
- Round 0: await intent (~400ms), stream ack immediately as TTFT,
  then execute tool sequentially; chat-only streams directly
- IntentResult.ack: one-sentence acknowledgment, intent max_tokens 200→350
- _parse_intent extracts and trims ack field

KV cache stability (llm.py, generation_buffer.py, generation_task.py):
- build_context: replace cached_note_ids with include_note_ids
- Auto-found notes populate context_meta["auto_notes"] for sidebar but
  are NOT injected into system prompt (--- Related Notes --- removed)
- Explicitly included notes injected as --- Included Notes ---
- _conv_note_cache dict + get/set/clear functions removed from generation_buffer.py
- All clear_conv_note_cache() calls removed

Cold model retry (llm.py):
- generate_completion (used by classify_intent) retries on HTTP 500:
  3 attempts with 3s/6s delays — prevents intent failure during cold load

API + frontend (routes/chat.py, stores/chat.ts, views/ChatView.vue, components/ChatPanel.vue):
- exclude_note_ids → include_note_ids throughout
- ChatView sidebar: Suggested (auto-found, + to include) + In Context (× to remove)
- ChatPanel: remove exclude button from context pills; no IDs passed to sendMessage

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

src/fabledassistant/routes/chat.py

@@ -113,7 +113,7 @@ async def send_message_route(conv_id: int):
     if not content:
         return jsonify({"error": "content is required"}), 400
     context_note_id = data.get("context_note_id")
-    exclude_note_ids = data.get("exclude_note_ids") or []
+    include_note_ids = data.get("include_note_ids") or []
     think = bool(data.get("think", False))
 
     # Reject if generation already running for this conversation
@@ -142,7 +142,7 @@ async def send_message_route(conv_id: int):
         buf, history, model,
         uid, conv_id, conv.title, content,
         context_note_id=context_note_id,
-        exclude_note_ids=exclude_note_ids,
+        include_note_ids=include_note_ids,
         think=think,
     ))