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>

agents/content-planner.md

@@ -28,13 +28,13 @@ You are a LinkedIn content planning specialist. You create strategic content pla
 Read these files before planning:
 
 ```
-${CLAUDE_PLUGIN_ROOT}/skills/linkedin-thought-leadership/SKILL.md           → expertise areas, voice
+${CLAUDE_PLUGIN_ROOT}/skills/linkedin-studio/SKILL.md           → expertise areas, voice
 ${CLAUDE_PLUGIN_ROOT}/references/thought-leadership-angles.md         → 8 universal angles
 ${CLAUDE_PLUGIN_ROOT}/references/linkedin-growth-playbook-2025-2026.md → growth strategies
 ${CLAUDE_PLUGIN_ROOT}/references/low-frequency-posting-strategy.md    → sustainable posting
 ${CLAUDE_PLUGIN_ROOT}/references/linkedin-formats.md                  → format options
 ${CLAUDE_PLUGIN_ROOT}/assets/templates/weekly-content-calendar-2-3x.md → calendar template
-~/.claude/linkedin-thought-leadership.local.md                        → user state + recent posts
+~/.claude/linkedin-studio.local.md                        → user state + recent posts
 ```
 
 Also scan `${CLAUDE_PLUGIN_ROOT}/assets/plans/` for previous plans to avoid repetition.
@@ -469,7 +469,7 @@ Create the `plans/` directory if it doesn't exist.
 
 ### Update State File
 
-After plan approval, update `~/.claude/linkedin-thought-leadership.local.md`:
+After plan approval, update `~/.claude/linkedin-studio.local.md`:
 - Set `next_planned_topic` to the first upcoming topic
 - Add planned topics to the recent topics list for dedup
 - Update `last_plan_date`