refactor: use industry-standard shell-quote for argument parsing

- Replace custom parseShellArgs with battle-tested shell-quote package
- Simplify code by removing unnecessary -p filtering (Claude handles it)
- Update tests to use shell-quote directly
- Add example workflow showing claude_args usage

This provides more robust argument parsing while reducing code complexity.

base-action/package.json

@@ -10,11 +10,13 @@
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
-    "@actions/core": "^1.10.1"
+    "@actions/core": "^1.10.1",
+    "shell-quote": "^1.8.3"
   },
   "devDependencies": {
     "@types/bun": "^1.2.12",
     "@types/node": "^20.0.0",
+    "@types/shell-quote": "^1.7.5",
     "prettier": "3.5.3",
     "typescript": "^5.8.3"
   }