Merge remote-tracking branch 'origin/master' into gitea/feature/end

Resolved conflicts taking origin/master (v0.5.55) as canonical, with local
features re-applied:
- runtime log level (LOG_LEVEL env + dashboard Settings → Logging, applied
  immediately and persisted across restarts)
- free/noAuth provider enable/disable toggle via providerStrategies.enabled
- parallel model testing (Test All Models / Test Selected Keys)

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",