Add prepaid resource credits with prorated deploy billing.

When users delete an app before plan expiry, remaining resources become credits for a new deploy. The deploy calculator shows covered vs additional charges, prices optional services correctly, and prorates extras to days left on the credit.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/applications/entities/application.entity.ts

@@ -166,6 +166,14 @@ export class Application {
   @Column({ type: 'timestamptz', nullable: true })
   scheduledDeletionAt: Date; // When the app will be permanently deleted
 
+  /** When the user voluntarily removed the app (data docked for restore). */
+  @Column({ type: 'timestamptz', nullable: true })
+  dockedAt?: Date;
+
+  /** Snapshot captured at dock time — used to restore DB / wp-content / source. */
+  @Column({ nullable: true })
+  dockSnapshotId?: string;
+
   @CreateDateColumn()
   createdAt: Date;