feat(core): FK for user_id columns; MCP search requires user

- Add fk_entries_user_id, fk_entries_history_user_id, fk_audit_log_user_id (ON DELETE SET NULL)
- Add scripts/cleanup-orphan-user-ids.sql for pre-deploy orphan user_id cleanup
- Remove deprecated SERVER_MASTER_KEY / per-user key wrap helpers from secrets-core
- secrets-mcp: require authenticated user for secrets_search; improve body-read failure response
- Bump secrets-mcp to 0.2.1

Made-with: Cursor

scripts/cleanup-orphan-user-ids.sql

@@ -0,0 +1,22 @@
+-- Run against prod BEFORE deploying secrets-mcp with FK migration.
+-- Requires: write access to SECRETS_DATABASE_URL.
+-- Example: psql "$SECRETS_DATABASE_URL" -v ON_ERROR_STOP=1 -f scripts/cleanup-orphan-user-ids.sql
+
+BEGIN;
+
+UPDATE entries
+SET user_id = NULL
+WHERE user_id IS NOT NULL
+  AND NOT EXISTS (SELECT 1 FROM users u WHERE u.id = entries.user_id);
+
+UPDATE entries_history
+SET user_id = NULL
+WHERE user_id IS NOT NULL
+  AND NOT EXISTS (SELECT 1 FROM users u WHERE u.id = entries_history.user_id);
+
+UPDATE audit_log
+SET user_id = NULL
+WHERE user_id IS NOT NULL
+  AND NOT EXISTS (SELECT 1 FROM users u WHERE u.id = audit_log.user_id);
+
+COMMIT;