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>

src/scribe/services/tz.py

@@ -13,14 +13,11 @@ from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
 
 from scribe.services.settings import get_setting
 
-# Day-rollover boundary for journal/day-anchored views. The "day" flips at
+# Day-rollover boundary for day-anchored "today" logic. The "day" flips at
 # this local hour (not midnight) so the 00:00–04:00 local window still
 # shows yesterday's content until the user "starts" the new day.
 DAY_ROLLOVER_HOUR = 4
 
-# Backwards-compat alias for code paths still referencing the old name.
-BRIEFING_DAY_START_HOUR = DAY_ROLLOVER_HOUR
-
 
 async def get_user_tz(user_id: int) -> ZoneInfo:
     """Return the user's IANA ``ZoneInfo``, falling back to UTC."""
@@ -41,12 +38,8 @@ async def user_day_date(user_id: int) -> date:
     """Return the current "day" in the user's local timezone.
 
     The day flips at ``DAY_ROLLOVER_HOUR`` (4am local) rather than midnight,
-    so the 00:00–04:00 local window still returns *yesterday* — the user's
-    journal stays anchored to yesterday until they cross the rollover.
+    so the 00:00–04:00 local window still returns *yesterday* — a day-anchored
+    view stays on yesterday until the user crosses the rollover.
     """
     tz = await get_user_tz(user_id)
     return (datetime.now(tz) - timedelta(hours=DAY_ROLLOVER_HOUR)).date()
-
-
-# Backwards-compat alias used by briefing-only modules being torn down in Stage B.
-user_briefing_date = user_day_date