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/update-skills/SKILL.md

@@ -110,8 +110,8 @@ If a merge fails badly (e.g., cannot resolve conflicts):
 # Step 4: Validation
 
 After all selected skills are merged:
-- `npm run build`
-- `npm test` (do not fail the flow if tests are not configured)
+- `pnpm run build`
+- `pnpm test` (do not fail the flow if tests are not configured)
 
 If build fails:
 - Show the error.