feat: add auto-language detection support to stt-ptt

- Add STT_LANGUAGE environment variable (default: auto)
- Modify whisper-cli call to use -l flag with language code
- Add language option to HM module (enum with 23 common languages + auto)
- Update help text to document STT_LANGUAGE variable

modules/home-manager/cli/stt-ptt.nix

@@ -77,6 +77,56 @@ in {
       '';
       example = 5000;
     };
+
+    language = mkOption {
+      type = types.enum [
+        "auto"
+        "en"
+        "es"
+        "fr"
+        "de"
+        "it"
+        "pt"
+        "ru"
+        "zh"
+        "ja"
+        "ko"
+        "ar"
+        "hi"
+        "tr"
+        "pl"
+        "nl"
+        "sv"
+        "da"
+        "fi"
+        "no"
+        "vi"
+        "th"
+        "id"
+        "uk"
+        "cs"
+      ];
+      default = "auto";
+      description = ''
+        Language for speech recognition. Use "auto" for automatic language detection,
+        or specify a language code (ISO 639-1 standard) for better accuracy.
+
+        Auto-detection analyzes the audio to determine the spoken language automatically.
+        Specifying a language can improve accuracy if you know the language in advance.
+
+        Common language codes:
+        - en: English
+        - es: Spanish
+        - fr: French
+        - de: German
+        - zh: Chinese
+        - ja: Japanese
+        - ko: Korean
+
+        whisper.cpp supports 100+ languages. See whisper.cpp documentation for the full list.
+      '';
+      example = "en";
+    };
   };
 
   config = mkIf cfg.enable {
@@ -84,6 +134,7 @@ in {
 
     home.sessionVariables = {
       STT_MODEL = modelPath;
+      STT_LANGUAGE = cfg.language;
       STT_NOTIFY_TIMEOUT = toString cfg.notifyTimeout;
     };