fix(marketplace): update version/count and wire orphan skills into bundles (#60)

The Claude plugins marketplace reads .claude-plugin/marketplace.json, which
was stale (version 14.0.0, '167 skills') and three skills lived only in root
skills/ with no bundle, so they could never appear in the marketplace:

- Bump marketplace version 14.0.0 -> 20.2.0 and description 167 -> 174.
- Wire the orphan skills into their natural bundles (identical copies, matching
  the repo's dual-maintenance convention):
    youtube-script-writer  -> pm-writers      (1.0.0 -> 1.1.0)
    launch-readiness        -> pm-delivery     (3.2.0 -> 3.3.0)
    skill-security-auditor  -> pm-engineering  (4.1.0 -> 4.2.0)
- Add the missing pm-writers plugin.json manifest; bump the pm-delivery and
  pm-engineering manifests to match and mention the new skills.
- Regenerate exports (they move from other/ into the bundle folders) and web/skills.json.


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

Co-authored-by: Claude <noreply@anthropic.com>

plugins/pm-delivery/.claude-plugin/plugin.json

@@ -1,8 +1,8 @@
 {
   "$schema": "https://anthropic.com/claude-code/plugin.schema.json",
   "name": "pm-delivery",
-  "version": "3.0.0",
-  "description": "Sprint & delivery skills: Sprint Planning, Technical Spec Template, A/B Test Planner, Go-to-Market Planner, Product Launch Checklist, Sprint Brief, Retro Analysis.",
+  "version": "3.3.0",
+  "description": "Sprint & delivery skills: Sprint Planning, Technical Spec Template, A/B Test Planner, Go-to-Market Planner, Product Launch Checklist, Sprint Brief, Retro Analysis, User Story Writer, Launch Readiness.",
   "author": {
     "name": "Mohit Aggarwal",
     "email": "mohit15856@gmail.com"