Ignore Claude local files and enforce pnpm (#226)

* Ignore Claude local files

* Prohibit use of non-pnpm package managers

* Ensure EOF newline

.claude/.gitignore

@@ -0,0 +1,3 @@
+worktrees/
+*.local.*
+

package.json

@@ -7,6 +7,7 @@
   "scripts": {
     "dev": "vite",
     "build": "vite build",
+    "preinstall": "npx only-allow pnpm",
     "preview": "vite preview",
     "check": "svelte-check --tsconfig ./tsconfig.json",
     "prepare": "husky"