feat(db): add deletedAt audit timestamp to soft-deletable models

Add deletedAt DateTime? to User, Client, Role, Resource, and Blueprint
models for GDPR-compliant deactivation audit trail. Soft-delete mutations
now stamp deletedAt: new Date() on deactivation and clear it on
reactivation. Migration and test assertions updated accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/api/src/router/client-procedure-support.ts

@@ -199,7 +199,7 @@ export async function updateClient(ctx: ClientProcedureContext, input: ClientUpd
 export async function deactivateClient(ctx: ClientProcedureContext, input: ClientIdInput) {
   const updated = await ctx.db.client.update({
     where: { id: input.id },
-    data: { isActive: false },
+    data: { isActive: false, deletedAt: new Date() },
   });
 
   void createAuditEntry({