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/multiplatform.md

@@ -9,6 +9,7 @@ allowed-tools:
   - Read
   - Glob
   - Write
+  - Bash
   - AskUserQuestion
 ---
 
@@ -163,7 +164,11 @@ YouTube tips:
 
 After creating the adaptation:
 - Save to `${CLAUDE_PLUGIN_ROOT}/assets/drafts/multiplatform/[platform]-[slug].md`
-- Present copy-paste ready version
+- Auto-copy the adapted content to clipboard silently:
+```bash
+printf '%s' '<ADAPTED_CONTENT>' | node ${CLAUDE_PLUGIN_ROOT}/hooks/scripts/clipboard-helper.mjs
+```
+- Present the content and confirm: "Copied to clipboard."
 - Note platform-specific publishing tips
 
 ## Reference Files