Add Civitai metadata fetching functionality for checkpoints

- Implement fetchCivitai API method to retrieve metadata from Civitai.
- Enhance CheckpointsControls to include fetch from Civitai functionality.
- Update PageControls to register fetch from Civitai event listener for both LoRAs and Checkpoints.

static/js/components/controls/CheckpointsControls.js

@@ -1,6 +1,6 @@
 // CheckpointsControls.js - Specific implementation for the Checkpoints page
 import { PageControls } from './PageControls.js';
-import { loadMoreCheckpoints, resetAndReload, refreshCheckpoints } from '../../api/checkpointApi.js';
+import { loadMoreCheckpoints, resetAndReload, refreshCheckpoints, fetchCivitai } from '../../api/checkpointApi.js';
 import { showToast } from '../../utils/uiHelpers.js';
 
 /**
@@ -33,6 +33,11 @@ export class CheckpointsControls extends PageControls {
                 return await refreshCheckpoints();
             },
             
+            // Add fetch from Civitai functionality for checkpoints
+            fetchFromCivitai: async () => {
+                return await fetchCivitai();
+            },
+            
             // No clearCustomFilter implementation is needed for checkpoints
             // as custom filters are currently only used for LoRAs
             clearCustomFilter: async () => {