feat(tts): add Xiaomi MiMo text-to-speech support

Adds mimo-v2.5-tts as a Media Provider TTS through the existing
OpenAI-compatible chat-completions endpoint. Voice is selected via the
top-level audio.voice field, and an optional style/language hint is
threaded through tts.js -> ttsCore.js -> the new adapter.

public/i18n/literals/ja.json

@@ -12,6 +12,7 @@
   "Logout": "ログアウト",
   "Login": "ログイン",
   "Providers": "プロバイダー",
+  "Style": "スタイル",
   "Usage": "統計",
   "API Key": "APIキー",
   "Connected": "接続済み",
@@ -176,6 +177,7 @@
   "How it works:": "しくみ：",
   "Antigravity/Copilot IDE request → DNS redirect to localhost:443 → MITM proxy intercepts → 9Router → response to Antigravity/Copilot": "Antigravity/Copilot IDE リクエスト → localhost:443 への DNS リダイレクト → MITM プロキシが傍受 → 9Router → Antigravity/Copilot への応答",
   "No API keys — create one in Keys page": "APIキーがありません — キーページで1つ作成してください",
+  "e.g. a warm, gentle voice, speaking slowly with a British accent": "例：温かく穏やかな声で、イギリス英語のアクセントでゆっくり話す",
   "sk_9router (default)": "sk_9router（デフォルト）",
   "Server started": "サーバーが開始されました",
   "Failed to start server": "サーバーの開始に失敗しました",