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/react.md

@@ -12,6 +12,7 @@ allowed-tools:
   - Glob
   - Grep
   - WebFetch
+  - Bash
   - AskUserQuestion
 ---
 
@@ -135,6 +136,12 @@ Show:
 3. Suggested first comment (with the URL + brief context)
 4. Recommended posting time
 
+Auto-copy the main draft text to clipboard silently:
+```bash
+printf '%s' '<MAIN_DRAFT_TEXT>' | node ${CLAUDE_PLUGIN_ROOT}/hooks/scripts/clipboard-helper.mjs
+```
+Then confirm: "Copied to clipboard."
+
 Offer refinement options via AskUserQuestion:
 1. Perfect — ready to post
 2. Adjust the hook