feat(phase2): OAuth/Authentik integration + drag-and-drop reordering

- Add OIDC/OAuth2 login via openid-client with PKCE flow
- Auto-provision OAuth users with group mapping
- Conditional login page (OAuth/local/both based on auth mode)
- Admin OAuth test connection button
- Install svelte-dnd-action for board editor DnD
- Draggable sections and widgets with cross-section moves
- Reorder APIs with atomic Prisma transactions
- Visual drag handles and drop zone indicators

package.json

@@ -30,8 +30,10 @@
 		"jsonwebtoken": "^9.0.2",
 		"lucide-svelte": "^0.469.0",
 		"node-cron": "^3.0.3",
+		"openid-client": "^6.8.2",
 		"simple-icons": "^13.0.0",
 		"svelte": "^5.0.0",
+		"svelte-dnd-action": "^0.9.69",
 		"sveltekit-superforms": "^2.22.0",
 		"tailwind-merge": "^2.6.0",
 		"zod": "^3.24.0"