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/controls/CheckpointsControls.js

@@ -2,7 +2,7 @@
 import { PageControls } from './PageControls.js';
 import { loadMoreCheckpoints, resetAndReload, refreshCheckpoints, fetchCivitai } from '../../api/checkpointApi.js';
 import { showToast } from '../../utils/uiHelpers.js';
-import { CheckpointDownloadManager } from '../../managers/CheckpointDownloadManager.js';
+import { downloadManager } from '../../managers/DownloadManager.js';
 
 /**
  * CheckpointsControls class - Extends PageControls for Checkpoint-specific functionality
@@ -12,9 +12,6 @@ export class CheckpointsControls extends PageControls {
         // Initialize with 'checkpoints' page type
         super('checkpoints');
         
-        // Initialize checkpoint download manager
-        this.downloadManager = new CheckpointDownloadManager();
-        
         // Register API methods specific to the Checkpoints page
         this.registerCheckpointsAPI();
     }
@@ -44,7 +41,7 @@ export class CheckpointsControls extends PageControls {
             
             // Add show download modal functionality
             showDownloadModal: () => {
-                this.downloadManager.showDownloadModal();
+                downloadManager.showDownloadModal();
             },
             
             // No clearCustomFilter implementation is needed for checkpoints

static/js/components/controls/LorasControls.js

@@ -3,6 +3,7 @@ import { PageControls } from './PageControls.js';
 import { loadMoreLoras, fetchCivitai, resetAndReload, refreshLoras } from '../../api/loraApi.js';
 import { getSessionItem, removeSessionItem } from '../../utils/storageHelpers.js';
 import { createAlphabetBar } from '../alphabet/index.js';
+import { downloadManager } from '../../managers/DownloadManager.js';
 
 /**
  * LorasControls class - Extends PageControls for LoRA-specific functionality
@@ -46,11 +47,7 @@ export class LorasControls extends PageControls {
             },
             
             showDownloadModal: () => {
-                if (window.downloadManager) {
-                    window.downloadManager.showDownloadModal();
-                } else {
-                    console.error('Download manager not available');
-                }
+                downloadManager.showDownloadModal();
             },
             
             toggleBulkMode: () => {