feat(media-hosting): add multi-provider configurable upload with fallback

Add Random/Preferred/None modes, preferred provider selection, and provider-order fallback. Catbox/Imgur/PostImages on Android via WebView; Electron CDP automation for Imgur/PostImages. Hide upload controls on web runtime.

src/plugins/file-uploader.ts

@@ -1,7 +1,19 @@
 import { registerPlugin } from '@capacitor/core';
+import type { ProviderAttempt, ProviderId } from '../lib/media-hosting/types';
+
+export interface PickAndUploadMediaOptions {
+  providerOrder: ProviderId[];
+}
+
+export interface PickAndUploadMediaResult {
+  url: string;
+  fileName: string;
+  provider: ProviderId;
+  attempts?: ProviderAttempt[];
+}
 
 export interface FileUploaderPlugin {
-  pickAndUploadMedia(): Promise<{ url: string; fileName: string }>;
+  pickAndUploadMedia(options?: PickAndUploadMediaOptions): Promise<PickAndUploadMediaResult>;
 }
 
 const FileUploader = registerPlugin<FileUploaderPlugin>('FileUploader');