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/de.json

@@ -12,6 +12,7 @@
   "Logout": "Abmelden",
   "Login": "Anmelden",
   "Providers": "Anbieter",
+  "Style": "Stil",
   "Usage": "Statistiken",
   "API Key": "API-Schlüssel",
   "Connected": "Verbunden",
@@ -176,6 +177,7 @@
   "How it works:": "So funktioniert es:",
   "Antigravity/Copilot IDE request → DNS redirect to localhost:443 → MITM proxy intercepts → 9Router → response to Antigravity/Copilot": "Antigravity/Copilot IDE-Anforderung → DNS-Umleitung auf localhost:443 → MITM-Proxy abfangen → 9Router → Antwort auf Antigravity/Copilot",
   "No API keys — create one in Keys page": "Keine API-Schlüssel — erstellen Sie einen auf der Seite Schlüssel",
+  "e.g. a warm, gentle voice, speaking slowly with a British accent": "z. B.: eine warme, sanfte Stimme, die langsam mit britischem Akzent spricht",
   "sk_9router (default)": "sk_9router (Standard)",
   "Server started": "Server gestartet",
   "Failed to start server": "Server konnte nicht gestartet werden",