Remove CalDAV todo tools; overhaul quick-capture

- Remove all 6 CalDAV todo tools (create/list/update/complete/delete/search_todos)
  from tools.py definitions, imports, execute_tool branches, intent routing rules,
  generation_task labels/actions, and llm.py system prompt hints. CalDAV event
  tools remain. Todo functions still exist in caldav.py but are no longer exposed.

- Quick-capture now uses a dedicated classify_capture_intent() with a focused
  _CAPTURE_SYSTEM_PROMPT that always routes to a tool (never null). Tool set
  expanded: create_note/task/event + update_note + research_topic.

- research_topic in quick-capture calls run_research_pipeline() directly (no SSE
  buffer). run_research_pipeline() now accepts buf=None; all buf.append_event
  calls are guarded so status events are skipped when no buffer is provided.

- Fallback note now always sets body=text (was empty for texts ≤80 chars).

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

src/fabledassistant/services/llm.py

@@ -389,13 +389,10 @@ async def build_context(
     if has_caldav:
         tool_lines[-1] = (
             "Available actions: create_task, create_note, update_note, delete_note, delete_task, get_note, list_notes, list_tasks, search_notes, "
-            "create_event, list_events, search_events, update_event, delete_event, "
-            "list_calendars, create_todo, list_todos, search_todos, update_todo, complete_todo, delete_todo."
+            "create_event, list_events, search_events, update_event, delete_event, list_calendars."
         )
         tool_lines.append("For calendar events, use ISO 8601 datetime format (e.g. 2026-09-30T00:00:00).")
-        tool_lines.append("CalDAV todos are separate from app tasks. Use create_task for app tasks, create_todo for CalDAV todos.")
         tool_lines.append("When the user says 'remind me' with a time before an event, use the reminder_minutes parameter.")
-        tool_lines.append("Use search_todos to find a specific CalDAV todo by keyword when list_todos would return too many results.")
     tool_lines.append("For relative dates like 'Friday' or 'next week', resolve them to YYYY-MM-DD format.")
     tool_lines.append("When creating notes, use the `tags` parameter — do not embed #tag text in the note body.")
     tool_lines.append(