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/setup.ts

@@ -1,7 +1,7 @@
-#!/usr/bin/env npx tsx
+#!/usr/bin/env pnpm exec tsx
 /**
  * X Integration - Authentication Setup
- * Usage: npx tsx setup.ts
+ * Usage: pnpm exec tsx setup.ts
  *
  * Interactive script - opens browser for manual login
  */