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>

frontend/src/views/CalendarView.vue

@@ -168,11 +168,11 @@ function onCalendarChanged() {
 
 onMounted(() => {
   document.addEventListener("mousedown", onDocClick);
-  document.addEventListener("fable:calendar-changed", onCalendarChanged);
+  document.addEventListener("scribe:calendar-changed", onCalendarChanged);
 });
 onUnmounted(() => {
   document.removeEventListener("mousedown", onDocClick);
-  document.removeEventListener("fable:calendar-changed", onCalendarChanged);
+  document.removeEventListener("scribe:calendar-changed", onCalendarChanged);
 });
 
 // ── Calendar callbacks ─────────────────────────────────────────────────────