feat: add audit logging for all admin actions and admin audit page

Log every admin-panel action (user activate/deactivate, team BYOC toggle,
team delete, template delete, build create/cancel) to the audit_logs table
under PlatformTeamID with scope "admin".

Add GET /v1/admin/audit-logs endpoint and /admin/audit frontend page with
infinite scroll and hierarchical filters. Expose audit.Entry + Log() for
cloud repo extensibility.

Fix seed_platform_team down-migration FK violation by deleting dependent
rows before the team row.

frontend/src/lib/components/AdminSidebar.svelte

@@ -13,7 +13,8 @@
 		IconChevron,
 		IconShield,
 		IconMembers,
-		IconUser
+		IconUser,
+		IconAudit
 	} from './icons';
 
 	let { collapsed = $bindable(false) }: { collapsed: boolean } = $props();
@@ -26,7 +27,8 @@
 
 	const managementItems: NavItem[] = [
 		{ label: 'Users', icon: IconUser, href: '/admin/users' },
-		{ label: 'Teams', icon: IconMembers, href: '/admin/teams' }
+		{ label: 'Teams', icon: IconMembers, href: '/admin/teams' },
+		{ label: 'Audit', icon: IconAudit, href: '/admin/audit' }
 	];
 
 	const platformItems: NavItem[] = [