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>

docs/integration-test-guide.md

@@ -1,11 +1,11 @@
-# Integration Test Guide: LinkedIn Thought Leadership Plugin
+# Integration Test Guide: LinkedIn Studio Plugin
 
 Manual integration testing scenarios for commands, agents, and hooks in the plugin.
 
 ## Prerequisites
 
 Before testing, ensure:
-- [ ] `~/.claude/linkedin-thought-leadership.local.md` exists (create from `config/state-file.template.md`)
+- [ ] `~/.claude/linkedin-studio.local.md` exists (create from `config/state-file.template.md`)
 - [ ] Voice samples exist in `assets/voice-samples/authentic-voice-samples.md`
 - [ ] Quality scorecard exists at `assets/checklists/quality-scorecard.md`
 - [ ] Plugin is installed: appears in Claude Code's skill/command list
@@ -62,7 +62,7 @@ Before testing, ensure:
 **Goal:** Graceful handling when state file doesn't exist.
 
 **Steps:**
-1. Temporarily rename `~/.claude/linkedin-thought-leadership.local.md`
+1. Temporarily rename `~/.claude/linkedin-studio.local.md`
 2. Run `/linkedin:pipeline`
 3. Verify: no crash, reasonable fallback (e.g., "No posting data found. Starting fresh.")
 4. Complete the pipeline
@@ -220,7 +220,7 @@ Before testing, ensure:
 1. Run `/linkedin:pipeline` and create a post
 2. Note the topic and hook
 3. End the session (or let Stop hook fire)
-4. Read `~/.claude/linkedin-thought-leadership.local.md`
+4. Read `~/.claude/linkedin-studio.local.md`
 5. Verify:
    - `last_post_date` = today
    - `last_post_topic` = the topic used