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/components/ChatPanel.vue

@@ -29,8 +29,6 @@ const noteSearchResults = ref<{ id: number; title: string }[]>([]);
 const noteSearchLoading = ref(false);
 let noteSearchTimer: ReturnType<typeof setTimeout> | null = null;
 
-// Exclude tracking
-const excludedNoteIds = ref<Set<number>>(new Set());
 
 const streamingRendered = computed(() => {
   if (!store.streamingContent) return "";
@@ -65,11 +63,7 @@ async function sendMessage() {
   messageInput.value = "";
   resetTextareaHeight();
   scrollToBottom();
-  await store.sendMessage(
-    content,
-    contextNoteId,
-    excludedNoteIds.value.size ? [...excludedNoteIds.value] : undefined,
-  );
+  await store.sendMessage(content, contextNoteId);
   scrollToBottom();
 }
 
@@ -151,10 +145,6 @@ function removeAttachedNote() {
 function promoteAutoNote(note: { id: number; title: string }) {
   attachedNote.value = note;
 }
-
-function excludeAutoNote(noteId: number) {
-  excludedNoteIds.value = new Set([...excludedNoteIds.value, noteId]);
-}
 </script>
 
 <template>
@@ -198,11 +188,6 @@ function excludeAutoNote(noteId: number) {
                 @click="promoteAutoNote(note)"
                 title="Attach for next message"
               >+</button>
-              <button
-                class="context-pill-btn exclude"
-                @click="excludeAutoNote(note.id)"
-                title="Exclude from auto-search"
-              >&times;</button>
             </span>
           </div>
 
@@ -463,9 +448,6 @@ function excludeAutoNote(noteId: number) {
 .context-pill-btn.promote:hover {
   color: var(--color-primary);
 }
-.context-pill-btn.exclude:hover {
-  color: var(--color-danger, #e74c3c);
-}
 
 /* Input wrapper */
 .panel-input-wrapper {