Phase 2: Core transcription pipeline and audio playback

- Implement faster-whisper TranscribeService with word-level timestamps,
  progress reporting, and hardware auto-detection
- Wire up Rust SidecarManager for Python process lifecycle (spawn, IPC, shutdown)
- Add transcribe_file Tauri command bridging frontend to Python sidecar
- Integrate wavesurfer.js WaveformPlayer with play/pause, skip, seek controls
- Build TranscriptEditor with word-level click-to-seek and active highlighting
- Connect file import flow: prompt → asset load → transcribe → display
- Add typed tauri-bridge service with TranscriptionResult interface
- Add Python tests for hardware detection and transcription result formatting

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/sidecar/ipc.rs

@@ -0,0 +1,16 @@
+use std::io::Write;
+
+use super::messages::IPCMessage;
+
+/// Serialize and write an IPC message to a writer (stdin pipe).
+pub fn send_message<W: Write>(writer: &mut W, msg: &IPCMessage) -> Result<(), String> {
+    let json = serde_json::to_string(msg).map_err(|e| e.to_string())?;
+    writer
+        .write_all(json.as_bytes())
+        .map_err(|e| format!("Write error: {e}"))?;
+    writer
+        .write_all(b"\n")
+        .map_err(|e| format!("Write error: {e}"))?;
+    writer.flush().map_err(|e| format!("Flush error: {e}"))?;
+    Ok(())
+}