fix: use process.cwd() for generate-review-builtin cwd on Windows

URL pathname returns /E:/... on Windows which spawnSync can't resolve.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

build.ts

@@ -13,7 +13,7 @@ console.log('Generating review builtin files...')
 const { spawnSync: genSpawnSync } = await import('child_process')
 const genResult = genSpawnSync('bun', ['run', 'scripts/generate-review-builtin.ts'], {
   stdio: 'inherit',
-  cwd: new URL('.', import.meta.url).pathname,
+  cwd: process.cwd(),
 })
 if (genResult.status !== 0) {
   console.warn('Warning: generate-review-builtin.ts failed, using existing files')