refactor(linkedin)!: rename plugin linkedin-thought-leadership → linkedin-studio (v3.0.0)

BREAKING CHANGE: the marketplace slug, the agent namespace
(linkedin-studio:<agent>), and the runtime state-file path
(~/.claude/linkedin-studio.local.md) all change. Reinstall required;
existing state migrated in place (post metrics, streak, history preserved).
The /linkedin:* commands are unchanged — the command namespace is set
per-command in frontmatter and was always independent of the plugin slug.
Functionality is byte-identical to v2.4.0; this release is pure identity.

- dir + manifests: plugins/linkedin-studio + plugin.json + root marketplace.json
- agent namespace updated in commands/newsletter.md (only functional invoker)
- state path updated in 4 hook scripts + topic-rotation prompt + state template
- catch-all skill dir renamed skills/linkedin-studio (5 functional skills unchanged)
- docs + version bump to 3.0.0 across README badge, CHANGELOG, root README/CLAUDE.md
- historical records (CHANGELOG past entries, docs/ build artifacts,
  config-audit v5.0.0 snapshots) intentionally retain the old slug

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

commands/ab-test.md

@@ -40,7 +40,7 @@ ls -1 ${CLAUDE_PLUGIN_ROOT}/assets/analytics/ab-tests/ 2>/dev/null | head -20
 ls -1 ${CLAUDE_PLUGIN_ROOT}/assets/analytics/posts/ 2>/dev/null | grep -E '\.json$' | head -10
 ```
 
-If `~/.claude/linkedin-thought-leadership.local.md` exists, read it for user context (posting frequency, follower level, topics).
+If `~/.claude/linkedin-studio.local.md` exists, read it for user context (posting frequency, follower level, topics).
 
 ## Step 1: Determine Intent