Add three new frontend routes to support HTMX-powered modal dialogs:
1. GET /collections/create-modal
- Renders empty collection creation modal
- Uses CollectionModal template with empty CollectionData
2. GET /collections/:id/edit-modal
- Fetches collection by ID from database
- Pre-populates modal with existing collection data
- Returns 400 for invalid UUID, 404 if collection not found
3. GET /collections/restore-modal
- Renders system collection restoration modal
- Allows users to restore deleted system collections
Route registration order:
- /collections/:id/edit-modal must be registered before /collections/:id
to avoid path conflicts in Echo's router
These routes enable the collections page to load modals dynamically via
HTMX (hx-get) instead of embedding modal HTML in the base page.