fix: rss classifier think-tag stripping, briefing calendar dict access, embed empty-string guard

- rss_classifier: strip <think>...</think> blocks (qwen3 reasoning output)
  before JSON parse; use strict=False for control chars; bump timeout 30s→120s
- briefing_pipeline: list_events returns dicts not Event objects — fix
  attribute access (.all_day/.start_dt/.title) to dict access
- embeddings: guard upsert_note_embedding and semantic_search_notes against
  empty-string input to prevent Ollama embed 400 errors

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

src/fabledassistant/services/briefing_pipeline.py

@@ -172,14 +172,18 @@ async def _gather_internal(user_id: int) -> dict:
             user_id=user_id, date_from=day_start, date_to=day_end
         )
         for e in internal_events:
-            if e.all_day:
+            if e.get("all_day"):
                 time_str = "all day"
-            elif e.start_dt:
-                local_dt = e.start_dt.astimezone(user_tz) if e.start_dt.tzinfo else e.start_dt.replace(tzinfo=timezone.utc).astimezone(user_tz)
+            elif e.get("start_dt"):
+                from datetime import datetime as _dt
+                start = e["start_dt"]
+                if isinstance(start, str):
+                    start = _dt.fromisoformat(start)
+                local_dt = start.astimezone(user_tz) if start.tzinfo else start.replace(tzinfo=timezone.utc).astimezone(user_tz)
                 time_str = local_dt.strftime("%-I:%M %p")
             else:
                 time_str = "unknown time"
-            calendar_events.append(f"{e.title} at {time_str}")
+            calendar_events.append(f"{e.get('title', 'Event')} at {time_str}")
     except Exception:
         logger.warning("Failed to gather internal calendar events for briefing", exc_info=True)
     # Also pull CalDAV events (deduped)