chore: remove pre-pivot dead code + finish Scribe rebrand (#599 t1-3)

- Header wordmark Fabled -> Scribe; fable:calendar-changed event ->
  scribe:calendar-changed; SettingsView CSS comment.
- Drop dead Project.auto_summary + summary_updated_at columns (migration
  0063) -- the Ollama-era summarizer is gone; model + 2 frontend types +
  projects test updated.
- Remove pivot vestiges: diagnostics _curator_busy()/curator_busy
  heartbeat field, tz BRIEFING_DAY_START_HOUR/user_briefing_date dead
  aliases, the ignored 'model' param on get_embedding (+ its test).

ruff src/ clean; CI is the gate. Part of scribe plan #599.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_mcp_tool_projects.py

@@ -20,7 +20,7 @@ def _bind_user():
 def _fake_project(**overrides) -> MagicMock:
     p = MagicMock()
     base = {"id": 1, "title": "P", "description": "", "goal": "",
-            "status": "active", "color": None, "auto_summary": None}
+            "status": "active", "color": None}
     base.update(overrides)
     p.to_dict.return_value = base
     return p