feat(youtube): extract transcript highlights like Reddit comment gems

Add extract_transcript_highlights() that scores sentences by specificity
(numbers, proper nouns, topic relevance) and filters YouTube filler
(subscribe, welcome back, etc). Top 5 highlights shown as structured
bullets in compact output. Full transcript moved to collapsible <details>
block so the LLM reads highlights first, full text on demand.

SKILL.md updated to instruct the judge agent to quote highlights
directly in synthesis, same as Reddit top comments.

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

scripts/lib/normalize.py

@@ -193,6 +193,7 @@ def normalize_youtube_items(
             date_confidence="high",
             engagement=engagement,
             transcript_snippet=item.get("transcript_snippet", ""),
+            transcript_highlights=item.get("transcript_highlights", []),
             relevance=item.get("relevance", 0.7),
             why_relevant=item.get("why_relevant", ""),
         ))