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/first-post.md

@@ -9,6 +9,7 @@ description: |
 allowed-tools:
   - Read
   - Write
+  - Bash
   - AskUserQuestion
 ---
 
@@ -135,17 +136,12 @@ Show the post with:
 - The hook highlighted
 - One alternative version with a different hook
 
-Format the post in a copy-paste-ready block:
-
-```
-=== COPY FROM HERE ===
-
-[post content]
-
-=== TO HERE ===
+Auto-copy the post text to clipboard silently:
+```bash
+printf '%s' '<POST_TEXT>' | node ${CLAUDE_PLUGIN_ROOT}/hooks/scripts/clipboard-helper.mjs
 ```
 
-Add: "Copy this text, go to linkedin.com, click 'Start a post', paste it, and hit Post."
+Then present: "Post copied to clipboard. Go to linkedin.com, click 'Start a post', paste it, and hit Post."
 
 ## Step 7: State Update