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>

frontend/src/stores/chat.ts

@@ -119,7 +119,7 @@ export const useChatStore = defineStore("chat", () => {
   async function sendMessage(
     content: string,
     contextNoteId?: number | null,
-    excludeNoteIds?: number[],
+    includeNoteIds?: number[],
     think = false,
     contextNoteTitle?: string,
   ) {
@@ -167,7 +167,7 @@ export const useChatStore = defineStore("chat", () => {
         {
           content,
           context_note_id: contextNoteId,
-          exclude_note_ids: excludeNoteIds?.length ? excludeNoteIds : undefined,
+          include_note_ids: includeNoteIds?.length ? includeNoteIds : undefined,
           think,
         },
       );