Preserve word-level timing on spelling edits

When the edited text has the same word count as the original (e.g. fixing
"Whisper" to "wisper"), each word keeps its original start/end timestamps.
Only falls back to segment-level timing when words are added or removed.

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

src/lib/components/TranscriptEditor.svelte

@@ -60,13 +60,19 @@
   function finishEditing(segmentId: string) {
     const trimmed = editText.trim();
     if (trimmed) {
-      // Update the segment text and rebuild words from the edited text.
-      // The display renders segment.words, so we must update them too.
       segments.update(segs => segs.map(s => {
         if (s.id !== segmentId) return s;
-        // Rebuild words from the edited text, preserving timing from the
-        // original segment boundaries (individual word timing is lost on edit)
-        const newWords = trimmed.split(/\s+/).map((word, widx) => ({
+        const newWordTexts = trimmed.split(/\s+/);
+        let newWords;
+        if (newWordTexts.length === s.words.length) {
+          // Same word count (e.g. spelling fix) — preserve each word's timing
+          newWords = s.words.map((w, widx) => ({
+            ...w,
+            word: newWordTexts[widx],
+          }));
+        } else {
+          // Word count changed — fall back to segment-level timing
+          newWords = newWordTexts.map((word, widx) => ({
             id: `${s.id}-word-${widx}`,
             segment_id: s.id,
             word,
@@ -75,6 +81,7 @@
             confidence: 1.0,
             word_index: widx,
           }));
+        }
         return {
           ...s,
           text: trimmed,