fix(database): restrict db delete to agent-owning org (system agents admin-only)

- UI: delete button gated by canDeleteDatabases prop threaded from each page
  (org page: only org-created agents; admin page: system agents)
- authz: org path requires agent.organizationId === active org; drop join-based
  attribution so a system agent merely linked to an org is admin-delete-only

src/features/database/actions/database-delete.action.ts

@@ -35,11 +35,7 @@ async function assertCanDeleteDatabase(databaseId: string): Promise<void> {
     const database = await db.query.database.findFirst({
         where: eq(drizzleDb.schemas.database.id, databaseId),
         with: {
-            agent: {
-                with: {
-                    organizations: true,
-                },
-            },
+            agent: true,
         },
     });
 
@@ -64,10 +60,11 @@ async function assertCanDeleteDatabase(databaseId: string): Promise<void> {
         const canManage = activeMember
             ? computeOrganizationPermissions(activeMember).canManageAgents
             : false;
+        // Only the organization that CREATED the agent may delete its databases.
+        // A system agent merely attributed to an org via the join table is
+        // handled by the isAdmin branch above (agent.organizationId === null).
         const hasAccess =
-            !!organization &&
-            (agent.organizationId === organization.id ||
-                agent.organizations.some((o) => o.organizationId === organization.id));
+            !!organization && agent.organizationId === organization.id;
         authorized = canManage && hasAccess;
     }