docs: convert all skill instructions from npm to pnpm

Batch update 62 files across .claude/skills/ — SKILL.md, REMOVE.md,
and script files. Conversions: npm run -> pnpm run, npm install ->
pnpm install, npx -> pnpm exec/dlx, npm uninstall -> pnpm uninstall,
package-lock.json -> pnpm-lock.yaml, shebangs updated.

.claude/skills/x-integration/scripts/post.ts

@@ -1,7 +1,7 @@
-#!/usr/bin/env npx tsx
+#!/usr/bin/env pnpm exec tsx
 /**
  * X Integration - Post Tweet
- * Usage: echo '{"content":"Hello world"}' | npx tsx post.ts
+ * Usage: echo '{"content":"Hello world"}' | pnpm exec tsx post.ts
  */
 
 import { getBrowserContext, runScript, validateContent, config, ScriptResult } from '../lib/browser.js';