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/services/generation_buffer.py

@@ -75,26 +75,6 @@ class GenerationBuffer:
 # Module-level singleton registry
 _buffers: dict[int | str, GenerationBuffer] = {}
 
-# Per-conversation note context cache — maps conv_id → sorted list of note IDs.
-# Stores the note IDs that were last included in the system prompt so that
-# subsequent turns in the same conversation can reuse them, stabilizing the
-# system prompt prefix and improving Ollama's KV cache hit rate.
-_conv_note_cache: dict[int, list[int]] = {}
-
-
-def get_conv_note_cache(conv_id: int) -> list[int]:
-    """Return cached note IDs for a conversation (empty list if none)."""
-    return list(_conv_note_cache.get(conv_id, []))
-
-
-def set_conv_note_cache(conv_id: int, note_ids: list[int]) -> None:
-    """Store note IDs to reuse on the next turn of this conversation."""
-    _conv_note_cache[conv_id] = list(note_ids)
-
-
-def clear_conv_note_cache(conv_id: int) -> None:
-    """Invalidate the note cache for a conversation (e.g. after a note write)."""
-    _conv_note_cache.pop(conv_id, None)
 _cleanup_task: asyncio.Task | None = None
 _GRACE_PERIOD = 60.0  # seconds to keep completed buffers