refactor: unify model download system across all model types

- Add download-related methods to baseModelApi.js for fetching versions, roots, folders, and downloading models
- Replace separate download managers with a unified DownloadManager.js supporting all model types
- Create a single download_modals.html template that adapts to model type (LoRA, checkpoint, etc.)
- Remove old download modals from lora_modals.html and checkpoint_modals.html
- Update apiConfig.js to include civitaiVersions endpoints for each model type
- Centralize event handler binding in DownloadManager.js (no more inline HTML handlers)
- Modal UI and logic now auto-adapt to the current model type, making future extension easier

static/js/components/ContextMenu/CheckpointContextMenu.js

@@ -3,7 +3,7 @@ import { ModelContextMenuMixin } from './ModelContextMenuMixin.js';
 import { resetAndReload } from '../../api/checkpointApi.js';
 import { getModelApiClient } from '../../api/baseModelApi.js';
 import { showToast } from '../../utils/uiHelpers.js';
-import { showExcludeModal } from '../../utils/modalUtils.js';
+import { showDeleteModal, showExcludeModal } from '../../utils/modalUtils.js';
 
 export class CheckpointContextMenu extends BaseContextMenu {
     constructor() {
@@ -42,10 +42,7 @@ export class CheckpointContextMenu extends BaseContextMenu {
                 apiClient.replaceModelPreview(this.currentCard.dataset.filepath);
                 break;
             case 'delete':
-                // Delete checkpoint
-                if (this.currentCard.querySelector('.fa-trash')) {
-                    this.currentCard.querySelector('.fa-trash').click();
-                }
+                showDeleteModal(this.currentCard.dataset.filepath);
                 break;
             case 'copyname':
                 // Copy checkpoint name