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/terminal/SttButton.tsx

@@ -0,0 +1,107 @@
+import { useCallback, useEffect, useRef, useState } from "react";
+import { useSTT } from "../../hooks/useSTT";
+import * as commands from "../../lib/tauri-commands";
+
+interface Props {
+  sessionId: string;
+  sendInput: (sessionId: string, data: string) => Promise<void>;
+}
+
+export default function SttButton({ sessionId, sendInput }: Props) {
+  const { state, error, toggle, cancelRecording } = useSTT(sessionId, sendInput);
+  const [elapsed, setElapsed] = useState(0);
+  const timerRef = useRef<ReturnType<typeof setInterval> | null>(null);
+
+  // Track recording duration
+  useEffect(() => {
+    if (state === "recording") {
+      setElapsed(0);
+      timerRef.current = setInterval(() => setElapsed((e) => e + 1), 1000);
+    } else {
+      if (timerRef.current) {
+        clearInterval(timerRef.current);
+        timerRef.current = null;
+      }
+    }
+    return () => {
+      if (timerRef.current) clearInterval(timerRef.current);
+    };
+  }, [state]);
+
+  const handleClick = useCallback(async () => {
+    // Auto-start STT container if not running
+    if (state === "idle") {
+      try {
+        const status = await commands.getSttStatus();
+        if (!status.running) {
+          await commands.startStt();
+        }
+      } catch {
+        // Container start failed, toggle will still attempt transcription
+      }
+    }
+    await toggle();
+  }, [state, toggle]);
+
+  const handleContextMenu = useCallback(
+    (e: React.MouseEvent) => {
+      e.preventDefault();
+      if (state === "recording") {
+        cancelRecording();
+      }
+    },
+    [state, cancelRecording],
+  );
+
+  const formatTime = (seconds: number) => {
+    const m = Math.floor(seconds / 60);
+    const s = seconds % 60;
+    return `${m}:${s.toString().padStart(2, "0")}`;
+  };
+
+  return (
+    <div className="absolute bottom-4 left-4 z-50 flex items-center gap-2">
+      <button
+        onClick={handleClick}
+        onContextMenu={handleContextMenu}
+        disabled={state === "transcribing"}
+        className={`w-8 h-8 rounded-full flex items-center justify-center transition-all cursor-pointer ${
+          state === "recording"
+            ? "bg-[#f85149] text-white shadow-lg animate-pulse"
+            : state === "transcribing"
+              ? "bg-[#1f2937] text-[#58a6ff] border border-[#30363d] opacity-80"
+              : "bg-[#1f2937]/80 text-[#8b949e] border border-[#30363d] hover:text-[#e6edf3] hover:bg-[#2d3748]"
+        }`}
+        title={
+          state === "recording"
+            ? "Click to stop and transcribe (right-click to cancel)"
+            : state === "transcribing"
+              ? "Transcribing..."
+              : "Speech to text"
+        }
+      >
+        {state === "transcribing" ? (
+          <svg className="w-4 h-4 animate-spin" viewBox="0 0 24 24" fill="none">
+            <circle cx="12" cy="12" r="10" stroke="currentColor" strokeWidth="2" opacity="0.25" />
+            <path d="M12 2a10 10 0 0 1 10 10" stroke="currentColor" strokeWidth="2" strokeLinecap="round" />
+          </svg>
+        ) : (
+          <svg className="w-4 h-4" viewBox="0 0 24 24" fill="currentColor">
+            <path d="M12 14c1.66 0 3-1.34 3-3V5c0-1.66-1.34-3-3-3S9 3.34 9 5v6c0 1.66 1.34 3 3 3z" />
+            <path d="M17 11c0 2.76-2.24 5-5 5s-5-2.24-5-5H5c0 3.53 2.61 6.43 6 6.92V21h2v-3.08c3.39-.49 6-3.39 6-6.92h-2z" />
+          </svg>
+        )}
+      </button>
+      {state === "recording" && (
+        <span className="text-xs text-[#f85149] font-mono bg-[#1f2937] px-2 py-0.5 rounded border border-[#30363d]">
+          {formatTime(elapsed)}
+        </span>
+      )}
+      {state === "error" && error && (
+        <span className="text-xs text-[#f85149] bg-[#1f2937] px-2 py-0.5 rounded border border-[#30363d] max-w-[200px] truncate">
+          {error}
+        </span>
+      )}
+    </div>
+  );
+}