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>

app/src/components/settings/SettingsPanel.tsx

@@ -9,6 +9,7 @@ import { detectHostTimezone } from "../../lib/tauri-commands";
 import type { EnvVar } from "../../lib/types";
 import Tooltip from "../ui/Tooltip";
 import WebTerminalSettings from "./WebTerminalSettings";
+import SttSettings from "./SttSettings";
 
 export default function SettingsPanel() {
   const { appSettings, saveSettings } = useSettings();
@@ -120,6 +121,9 @@ export default function SettingsPanel() {
       {/* Web Terminal */}
       <WebTerminalSettings />
 
+      {/* Speech to Text */}
+      <SttSettings />
+
       {/* Updates section */}
       <div>
         <label className="block text-sm font-medium mb-2">Updates<Tooltip text="Check for new versions of the Triple-C app and container image." /></label>