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/stores/use-media-hosting-store.ts

@@ -1,23 +1,44 @@
 import { create } from 'zustand';
 import { persist } from 'zustand/middleware';
+import type { ProviderId, UploadMode } from '../lib/media-hosting/types';
+import { MEDIA_HOSTING_PROVIDERS as PROVIDER_REGISTRY } from '../lib/media-hosting/providers';
 
-export const MEDIA_HOSTING_PROVIDERS = [{ id: 'catbox', name: 'Catbox', url: 'https://catbox.moe' }] as const;
-
-export type MediaHostingSelection = (typeof MEDIA_HOSTING_PROVIDERS)[number]['id'] | 'none' | string;
+/** Provider registry for UI: id, label, homepage URL, runtime support */
+export const MEDIA_HOSTING_PROVIDERS = PROVIDER_REGISTRY;
 
 interface MediaHostingStore {
-  selectedProvider: MediaHostingSelection;
-  setSelectedProvider: (provider: string) => void;
+  uploadMode: UploadMode;
+  preferredProvider: ProviderId;
+  setUploadMode: (mode: UploadMode) => void;
+  setPreferredProvider: (provider: ProviderId) => void;
+}
+
+const PERSIST_VERSION = 2;
+
+function migrate(_state: unknown): MediaHostingStore {
+  return {
+    uploadMode: 'random',
+    preferredProvider: 'catbox',
+  } as MediaHostingStore;
 }
 
 const useMediaHostingStore = create<MediaHostingStore>()(
   persist(
     (set) => ({
-      selectedProvider: 'catbox',
-      setSelectedProvider: (provider) => set({ selectedProvider: provider }),
+      uploadMode: 'random',
+      preferredProvider: 'catbox',
+      setUploadMode: (mode) => set({ uploadMode: mode }),
+      setPreferredProvider: (provider) => set({ preferredProvider: provider }),
     }),
     {
       name: 'media-hosting-storage',
+      version: PERSIST_VERSION,
+      migrate: (persistedState, version) => {
+        if (version < PERSIST_VERSION) {
+          return migrate(persistedState);
+        }
+        return persistedState as MediaHostingStore;
+      },
     },
   ),
 );