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-tauri/src/commands/project.rs

@@ -91,6 +91,16 @@ pub fn delete_project(id: String, state: State<AppState>) -> Result<(), String>
     queries::delete_project(&conn, &id).map_err(|e| e.to_string())
 }
 
+#[tauri::command]
+pub fn update_segment(
+    segment_id: String,
+    new_text: String,
+    state: State<AppState>,
+) -> Result<(), String> {
+    let conn = state.db.lock().map_err(|e| e.to_string())?;
+    queries::update_segment_text(&conn, &segment_id, &new_text).map_err(|e| e.to_string())
+}
+
 #[tauri::command]
 pub fn save_project_transcript(
     project_id: String,