docs(standards): add process.chdir() prohibition to code style

Added working directory rule to CLAUDE.md:
- Never use process.chdir() as it breaks tests, worker threads, and causes race conditions
- Always use { cwd } options and absolute paths instead
- Pass { cwd: absolutePath } to spawn/exec/fs operations

This rule prevents global state mutation anti-pattern that causes test failures in worker threads.

Author: jdalton

CLAUDE.md

@@ -146,6 +146,11 @@ TypeScript implementation of [Package URL specification](https://github.com/pack
   `import type { ArgParserConfig } from './argv.mjs'`
 - ❌ `import { parseScriptArgs, isQuiet, type ArgParserConfig } from './argv.mjs'`
 
+#### Working Directory
+- **🚨 NEVER use `process.chdir()`** - use `{ cwd }` options and absolute paths instead
+  - Breaks tests, worker threads, and causes race conditions
+  - Always pass `{ cwd: absolutePath }` to spawn/exec/fs operations
+
 #### Optional Properties
 With `exactOptionalPropertyTypes`, assign conditionally:
 - ✅ `if (value !== undefined) { this.prop = value }`