feat: add YouTube Script Writer skill (experimental) (#50) (#56)

Reapplies @prajwal-28's PR #50 onto current main WITHOUT the LF->CRLF
line-ending conversion the original PR introduced across skill-tiers.json
and the export indexes:
- adds skills/youtube-script-writer/SKILL.md (retention-optimized video scripts)
- registers it in the experimental tier
- regenerates the 5 platform exports with LF endings (no whole-file churn)



Claude-Session: https://claude.ai/code/session_016JWn5jRD5tcEFKrubjQ6Px

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: prajwal-28 <prajwal-28@users.noreply.github.com>

exports/cursor/README.md

@@ -3,7 +3,7 @@
 > Auto-generated from `skills/*/SKILL.md` by `scripts/build-exports.mjs`.
 > **Do not edit these files by hand** — edit the source skill and regenerate.
 
-173 skills exported. Copy a `.mdc rule` into the tool to use it.
+174 skills exported. Copy a `.mdc rule` into the tool to use it.
 
 | Skill | Bundle | Path |
 |---|---|---|
@@ -180,3 +180,4 @@
 | Vendor Evaluation | `pm-operations` | `pm-operations/vendor-evaluation/vendor-evaluation.mdc` |
 | Viral Content Framework | `pm-social` | `pm-social/viral-content-framework/viral-content-framework.mdc` |
 | Workshop Facilitation Guide | `pm-operations` | `pm-operations/workshop-facilitation-guide/workshop-facilitation-guide.mdc` |
+| YouTube Script Writer | `other` | `other/youtube-script-writer/youtube-script-writer.mdc` |