feat(tts): finish audio export with atomic temp-file pipeline (#18)

* feat(tts): finish audio export with atomic temp-file pipeline

* fix(tts): address audio export review findings

Author: TimInTech

app/i18n.py

@@ -94,7 +94,10 @@
         "tts.button.pause": "Pause",
         "tts.button.resume": "Fortsetzen",
         "tts.button.speak": "Vorlesen",
+        "tts.button.export": "Exportieren",
         "tts.button.stop": "Stopp",
+        "tts.export.dialog_title": "Audiodatei exportieren",
+        "tts.export.default_filename_prefix": "Blitztext-Audio_",
         "tts.error.piper_not_found": "Piper nicht gefunden. Installieren: pip install piper-tts und Stimmen nach ~/.local/share/piper-voices legen.",
         "tts.error.openai_not_available": "OpenAI Cloud-TTS ist nicht verfuegbar. Bitte OPENAI_API_KEY in ~/.config/blitztext-linux/secrets.env setzen.",
         "tts.consent.title": "OpenAI Cloud-TTS aktivieren?",
@@ -108,6 +111,11 @@
         "tts.status.synthesis": "Synthese…",
         "tts.status.openai_not_confirmed": "OpenAI Cloud-TTS wurde nicht bestaetigt.",
         "tts.status.cloud_synthesis": "Cloud-Synthese…",
+        "tts.status.exporting": "Exportiere Audiodatei…",
+        "tts.status.export_done": "Audiodatei exportiert.",
+        "tts.status.export_ffmpeg_missing": "ffmpeg nicht gefunden. Audio-Export ist nicht verfuegbar.",
+        "tts.status.export_format_unsupported": "Exportformat nicht unterstuetzt.",
+        "tts.status.missing_wav_output": "WAV-Ausgabe fehlt.",
         "tts.status.cancelled": "Abgebrochen.",
         "tts.status.error": "Fehler: {message}",
         "tts.status.done": "Fertig.",
@@ -245,7 +253,10 @@
         "tts.button.pause": "Pause",
         "tts.button.resume": "Resume",
         "tts.button.speak": "Read Aloud",
+        "tts.button.export": "Export",
         "tts.button.stop": "Stop",
+        "tts.export.dialog_title": "Export audio file",
+        "tts.export.default_filename_prefix": "blitztext-audio_",
         "tts.error.piper_not_found": "Piper not found. Install with: pip install piper-tts and place voices in ~/.local/share/piper-voices.",
         "tts.error.openai_not_available": "OpenAI Cloud-TTS is not available. Please set OPENAI_API_KEY in ~/.config/blitztext-linux/secrets.env.",
         "tts.consent.title": "Enable OpenAI Cloud-TTS?",
@@ -259,6 +270,11 @@
         "tts.status.synthesis": "Synthesizing…",
         "tts.status.openai_not_confirmed": "OpenAI Cloud-TTS was not confirmed.",
         "tts.status.cloud_synthesis": "Cloud synthesis…",
+        "tts.status.exporting": "Exporting audio file…",
+        "tts.status.export_done": "Audio file exported.",
+        "tts.status.export_ffmpeg_missing": "ffmpeg not found. Audio export is not available.",
+        "tts.status.export_format_unsupported": "Export format is not supported.",
+        "tts.status.missing_wav_output": "WAV output is missing.",
         "tts.status.cancelled": "Cancelled.",
         "tts.status.error": "Error: {message}",
         "tts.status.done": "Done.",