feat(audit): admin audit log

Audit log
- Add audit_log table (migration + schema) with index on created_at.
- Add auditLog service (writeAudit, getClientIp) and record events for backups
  (create, restore, upload-restore, delete, auto-settings), admin actions
  (users, OIDC, invites, system update, demo baseline, bag tracking, packing
  template delete, addons), and auth (app settings, MFA enable/disable).
- Add GET /api/admin/audit-log with pagination; fix invite insert row id lookup.
- Add AuditLogPanel and Admin tab; adminApi.auditLog.
- Add admin.tabs.audit and admin.audit.* strings in all locale files.
Note: Rebase feature branches so new DB migrations stay after existing ones
  (e.g. file_links) when merging upstream.

server/src/db/schema.ts

@@ -380,6 +380,17 @@ function createTables(db: Database.Database): void {
       UNIQUE(assignment_id, user_id)
     );
     CREATE INDEX IF NOT EXISTS idx_assignment_participants_assignment ON assignment_participants(assignment_id);
+
+    CREATE TABLE IF NOT EXISTS audit_log (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+      user_id INTEGER REFERENCES users(id) ON DELETE SET NULL,
+      action TEXT NOT NULL,
+      resource TEXT,
+      details TEXT,
+      ip TEXT
+    );
+    CREATE INDEX IF NOT EXISTS idx_audit_log_created ON audit_log(created_at DESC);
   `);
 }