Add speech-to-text feature using Faster Whisper container

Adds a mic button to the terminal UI that captures speech, transcribes
it via a Faster Whisper sidecar container, and injects the text into
the terminal input. Includes settings panel for model selection
(tiny/small/medium), port config, and container lifecycle management.

- stt-container/: Dockerfile + FastAPI server for Whisper transcription
- Rust backend: STT container management, transcribe_audio IPC command
- Frontend: useSTT hook, SttButton, SttSettings, WAV encoder
- CI: Gitea Actions workflow for multi-arch STT image builds

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

stt-container/Dockerfile

@@ -0,0 +1,13 @@
+FROM python:3.11-slim
+
+RUN pip install --no-cache-dir \
+    faster-whisper \
+    fastapi \
+    uvicorn[standard] \
+    python-multipart
+
+COPY server.py /app/server.py
+
+EXPOSE 9876
+
+CMD ["uvicorn", "app.server:app", "--host", "0.0.0.0", "--port", "9876"]