Persist segment text edits to database on Enter

- Add update_segment Tauri command (calls existing update_segment_text query)
- Wire onTextEdit handler from TranscriptEditor to invoke update_segment
- Edits are saved to SQLite immediately when user presses Enter

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

src/routes/+page.svelte

@@ -188,6 +188,14 @@
     waveformPlayer?.seekTo(timeMs);
   }
 
+  async function handleTextEdit(segmentId: string, newText: string) {
+    try {
+      await invoke('update_segment', { segmentId, newText });
+    } catch (err) {
+      console.error('Failed to save segment edit:', err);
+    }
+  }
+
   async function handleFileImport() {
     const filePath = await open({
       multiple: false,
@@ -512,7 +520,7 @@
   <div class="workspace">
     <div class="main-content">
       <WaveformPlayer bind:this={waveformPlayer} {audioUrl} />
-      <TranscriptEditor onWordClick={handleWordClick} />
+      <TranscriptEditor onWordClick={handleWordClick} onTextEdit={handleTextEdit} />
     </div>
     <div class="sidebar-right">
       <SpeakerManager />