feat(skills): add pdf-reader skill (#772)

Thanks @glifocat! Clean skill package — good docs, solid tests, nice intent files. Pushed a small fix for path traversal on the PDF filename before merging.

vitest.skills.config.ts

@@ -0,0 +1,7 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    include: ['.claude/skills/**/tests/*.test.ts'],
+  },
+});