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/ko.json

@@ -12,6 +12,7 @@
   "Logout": "로그아웃",
   "Login": "로그인",
   "Providers": "제공자",
+  "Style": "스타일",
   "Usage": "통계",
   "API Key": "API 키",
   "Connected": "연결됨",
@@ -176,6 +177,7 @@
   "How it works:": "작동 방식:",
   "Antigravity/Copilot IDE request → DNS redirect to localhost:443 → MITM proxy intercepts → 9Router → response to Antigravity/Copilot": "Antigravity/Copilot IDE 요청 → localhost:443로 DNS 리디렉션 → MITM 프록시가 가로챔 → 9Router → Antigravity/Copilot으로 응답",
   "No API keys — create one in Keys page": "API 키 없음 — 키 페이지에서 만들기",
+  "e.g. a warm, gentle voice, speaking slowly with a British accent": "예: 따뜻하고 부드러운 목소리로 영국식 억양을 쓰며 천천히 말하기",
   "sk_9router (default)": "sk_9router (기본값)",
   "Server started": "서버 시작됨",
   "Failed to start server": "서버 시작 실패",