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/dms/contracts.py

@@ -0,0 +1,22 @@
+"""DMS plugin contract — public interface for cross-plugin access."""
+
+from __future__ import annotations
+
+from app.plugins.builtins.dms.models import File as DmsFile, Folder
+
+
+class DmsContract:
+    """Public contract for the DMS plugin."""
+
+    DmsFile = DmsFile
+    Folder = Folder
+
+
+_contract_instance: DmsContract | None = None
+
+
+def get_contract() -> DmsContract:
+    global _contract_instance
+    if _contract_instance is None:
+        _contract_instance = DmsContract()
+    return _contract_instance