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/cs.json

@@ -12,6 +12,7 @@
   "Logout": "Odhlásit se",
   "Login": "Přihlásit se",
   "Providers": "Poskytovatelé",
+  "Style": "Styl",
   "Usage": "Statistika",
   "API Key": "Klíč API",
   "Connected": "Připojeno",
@@ -176,6 +177,7 @@
   "How it works:": "Jak to funguje:",
   "Antigravity/Copilot IDE request → DNS redirect to localhost:443 → MITM proxy intercepts → 9Router → response to Antigravity/Copilot": "Požadavek Antigravity/Copilot IDE → Přesměrování DNS na localhost:443 → Proxy MITM zachycuje → 9Router → odpověď na Antigravity/Copilot",
   "No API keys — create one in Keys page": "Žádné klíče API — vytvořte jeden na stránce Klíče",
+  "e.g. a warm, gentle voice, speaking slowly with a British accent": "např.: teplý, jemný hlas, mluvící pomalu s britským přízvukem",
   "sk_9router (default)": "sk_9router (výchozí)",
   "Server started": "Server spuštěn",
   "Failed to start server": "Spuštění serveru se nezdařilo",