pgAdmin 4: Missing authentication decorator on Constraints, preferences, Debugger and Schema Diff routes allows unauthenticated access in SERVER mode (incomplete fix for CVE-2026-12046)

In SERVER mode, pgAdmin 4 enforces authentication per route via the @pga_login_required decorator; the application's before_request hook only handles desktop-mode auto-login and the Kerberos/Webserver-auth redirect, so any route shipped without the decorator is reachable without authentication (CWE-306). This is the same defect class previously fixed as CVE-2026-12046 (the sqleditor close/update_connection routes). A follow-up sweep, prompted by a report describing an incomplete fix for CVE-2026-12046, found further routes missing @pga_login_required: the Constraints blueprint's nodes and proplist (object listing) routes and its delete route (a state-mutating DELETE that removes table constraints); preferences.get_all_cli (GET, discloses all CLI-settable preference values); debugger.close (DELETE); and schema_diff.close (DELETE). An unauthenticated network client could therefore enumerate constraint metadata, delete table constraints, read preference values, and force-close debugger or schema-diff sessions belonging to other users, without ever authenticating. Fix adds the missing @pga_login_required decorator (and the corresponding import to the Constraints module) to each of these routes. The change is decorator-only; no behavioral changes to the underlying handlers. This issue affects pgAdmin 4 in SERVER mode: the Constraints and Debugger routes from 1.0, the Schema Diff close route from 4.18, and preferences.get_all_cli from 8.2, all before 9.17.