feat(linkedin): add auto-clipboard on all content commands

Adds Bash to allowed-tools and clipboard-helper.mjs auto-copy to:
post.md, quick.md, react.md, pipeline.md, first-post.md,
video.md, multiplatform.md, carousel.md.

Each command auto-copies the final post/caption text to clipboard
after presenting the draft. Replaces manual copy-paste instructions
in first-post.md (=== COPY FROM HERE ===) with auto-copy.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/linkedin-thought-leadership/commands/carousel.md

@@ -8,6 +8,7 @@ description: |
   "linkedin carousel", "document post", "create slides".
 allowed-tools:
   - Read
+  - Bash
   - AskUserQuestion
 ---
 
@@ -129,6 +130,12 @@ Create one slide per page using the content above.
 Export as PDF and upload directly to LinkedIn.
 ```
 
+Auto-copy the carousel caption text to clipboard silently:
+```bash
+printf '%s' '<CAROUSEL_CAPTION>' | node ${CLAUDE_PLUGIN_ROOT}/hooks/scripts/clipboard-helper.mjs
+```
+Then confirm: "Caption copied to clipboard."
+
 Use AskUserQuestion: "Want to refine any slides, or is this ready for design?"
 
 ## Step 7: State Update