refactor(scribe): retire calendar/events + person/place/list entities (backend)

Narrow Scribe to a Claude-Code work system-of-record (milestone #194,
decision note #1759). Wholesale removal per rule #22 — backend + schema half.

Calendar/events + CalDAV: delete models/event, services/{events,caldav,
caldav_sync}, routes/events, mcp/tools/events; strip event branches from
backup (bump v3->v4), dashboard (upcoming_events), trash, recent, and the
mcp server read-only allowlist + instructions.

Typed entities (person/place/list): delete mcp/tools/entities; drop the
notes.metadata (entity_meta) column from model/service/routes and the
knowledge browse service. note_type STAYS — it also marks 'process' notes.

Scheduler: event_scheduler -> recurrence_scheduler, keeping only the
recurring-task spawn job (drops event reminders + CalDAV sync).

Schema: migration 0069 drops the events table + notes.metadata column +
orphan caldav settings rows (faithful downgrade recreates them).

KEEP: recurrence.py (task recurrence), notifications task reminders, graph
view, and every work surface. Frontend + plugin/docs true-up follow next.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BPtbSzA4JLMAKgFZ8VTg7Q

tests/test_services_backup.py

@@ -1,9 +1,9 @@
-"""Unit tests for the v3 backup export contract.
+"""Unit tests for the v4 backup export contract.
 
 CI runs pytest with no database, so these cover the parts that don't need one:
 the version/coverage constants, the pure join-table row helpers, and the export
 dict shape (via a mocked session). Full FK-remapping round-trip is exercised
-manually against a real DB (export a backup, confirm rulebooks/events appear).
+manually against a real DB (export a backup, confirm rulebooks appear).
 """
 from types import SimpleNamespace
 from unittest.mock import patch
@@ -13,8 +13,8 @@ import pytest
 from scribe.services import backup
 
 
-def test_backup_version_is_v3():
-    assert backup.BACKUP_VERSION == 3
+def test_backup_version_is_v4():
+    assert backup.BACKUP_VERSION == 4
 
 
 def test_not_included_lists_the_known_gaps():
@@ -61,12 +61,12 @@ async def test_export_full_backup_contains_v3_sections():
     with patch("scribe.services.backup.async_session", lambda: _CM()):
         out = await backup.export_full_backup()
 
-    assert out["version"] == 3
+    assert out["version"] == 4
     assert out["scope"] == "full"
     assert "api_keys" in out["_not_included"]
     # The sections v2 silently dropped must now be present (empty here).
     for key in ("rulebooks", "rulebook_topics", "rules",
                 "rulebook_subscriptions", "rule_suppressions",
-                "topic_suppressions", "events"):
+                "topic_suppressions"):
         assert key in out, f"missing v3 section: {key}"
         assert out[key] == []