feat: add ended_at column to aibridge_interceptions table (#20432)

Needed for marking interceptions as done
(https://github.com/coder/internal/issues/1051).

coderd/database/dump.sql

@@ -1055,7 +1055,8 @@ CREATE TABLE aibridge_interceptions (
     provider text NOT NULL,
     model text NOT NULL,
     started_at timestamp with time zone NOT NULL,
-    metadata jsonb
+    metadata jsonb,
+    ended_at timestamp with time zone
 );
 
 COMMENT ON TABLE aibridge_interceptions IS 'Audit log of requests intercepted by AI Bridge';