Security fixes: P0-P2 complete (22 fixes)

P0 (7): Auth-bypass removed, migrations fixed, plugin-upload disabled, RLS FORCE+WITH CHECK, plugin double-registration fixed, persistent volume, domain removed
P1 (11): User/tenant model, Redis centralized, worker separated, transactional outbox, XSS fixed, DMS chunked streaming, permissions unified, password reset, metrics secured, config/docs fixed, cross-tenant FK
P2 (4): Contact model normalized, cross-imports reduced 94%, commands+state machines for contacts/dms/mail/calendar, SPA path-traversal

8 new migrations, 99 unit tests, 13 commands, 8 contracts, 72 files changed

app/plugins/builtins/calendar/contracts.py

@@ -0,0 +1,23 @@
+"""Calendar plugin contract — public interface for cross-plugin access."""
+
+from __future__ import annotations
+
+from app.plugins.builtins.calendar.models import Calendar, CalendarEntry, CalendarEntryLink
+
+
+class CalendarContract:
+    """Public contract for the calendar plugin."""
+
+    Calendar = Calendar
+    CalendarEntry = CalendarEntry
+    CalendarEntryLink = CalendarEntryLink
+
+
+_contract_instance: CalendarContract | None = None
+
+
+def get_contract() -> CalendarContract:
+    global _contract_instance
+    if _contract_instance is None:
+        _contract_instance = CalendarContract()
+    return _contract_instance