Reduce perceived latency: move context build into task, title fire-and-forget, think:False on aux calls

- build_context() moved from route handler into run_generation() background task.
  The 202 response now returns immediately; client connects to SSE before
  note search / URL fetch begins, so 'Building context...' status is visible.
- _generate_title() runs in a fire-and-forget asyncio.create_task() after the
  'done' SSE event fires. Users see their response complete 2–5s sooner on new
  conversations; title appears later in the sidebar without blocking the stream.
- generate_completion() now sets think:False and accepts a max_tokens limit.
  Intent classifier passes max_tokens=200 (JSON only), title generator passes
  max_tokens=30 (short title), eliminating qwen3 thinking-mode overhead on these
  auxiliary calls.

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

src/fabledassistant/routes/chat.py

@@ -23,7 +23,6 @@ from fabledassistant.services.generation_buffer import (
     get_buffer,
 )
 from fabledassistant.services.generation_task import run_generation
-from fabledassistant.services.llm import build_context
 from fabledassistant.services.settings import get_setting
 
 logger = logging.getLogger(__name__)
@@ -127,17 +126,14 @@ async def send_message_route(conv_id: int):
         if msg.role != "system":
             history.append({"role": msg.role, "content": msg.content})
 
-    # Build context with note search, URL fetching, etc.
-    messages, context_meta = await build_context(
-        uid, history, context_note_id, content, exclude_note_ids=exclude_note_ids
-    )
-
     model = conv.model or await get_setting(uid, "default_model", Config.OLLAMA_MODEL)
 
-    # Launch background generation task
+    # Launch background generation task (context building happens inside the task)
     asyncio.create_task(run_generation(
-        buf, messages, model, context_meta,
+        buf, history, model,
         uid, conv_id, conv.title, content,
+        context_note_id=context_note_id,
+        exclude_note_ids=exclude_note_ids,
     ))
 
     return jsonify({