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

src/scribe/routes/knowledge.py

@@ -1,4 +1,4 @@
-"""Unified Knowledge endpoint — notes, people, places, lists in one queryable feed."""
+"""Unified Knowledge endpoint — notes, tasks, plans, and processes in one queryable feed."""
 import logging
 
 from quart import Blueprint, jsonify, request
@@ -10,7 +10,7 @@ logger = logging.getLogger(__name__)
 
 knowledge_bp = Blueprint("knowledge", __name__, url_prefix="/api/knowledge")
 
-_VALID_TYPES = {"note", "person", "place", "list", "task", "plan", "process"}
+_VALID_TYPES = {"note", "task", "plan", "process"}
 _VALID_SORTS = {"modified", "created", "alpha", "type"}
 
 
@@ -20,7 +20,7 @@ async def list_knowledge():
     """Return paginated knowledge objects with optional filtering.
 
     Query params:
-      type        — one of note|person|place|list (omit for all, excludes tasks)
+      type        — one of note|task|plan|process (omit for all)
       tags        — comma-separated tag filter (AND logic)
       sort        — modified|created|alpha|type (default: modified)
       q           — search query (semantic when provided, keyword fallback)