fix(test): isolate auto-update-checker mock.module() tests to prevent contamination

- Moved hook.test.ts, background-update-check.test.ts, workspace-resolution.test.ts, and cache.test.ts to separate sibling directories (_auc-mocks-hook, _auc-mocks-bg, _auc-mocks-ws, _auc-mocks-cache)
- Separated sync-package-json.test.ts to _auc-sync-mocks
- Fixed all relative import paths to account for new directory structure
- Bun runs same-directory test files in parallel; mock.module() calls contaminate each other. Only reliable isolation is separate directory = separate CI batch
- CI plan now creates individual isolated target for each mocking test file, preventing cross-file pollution

script/run-ci-tests.ts

@@ -82,7 +82,17 @@ async function runBunTest(testFiles: string[], label: string): Promise<void> {
   }
 
   console.log(`::group::${label}`)
-  const command = ["bun", "test", ...testFiles]
+  
+  // For directory paths, exclude _auc* directories which are separate isolated targets
+  const args = testFiles.map(tf => {
+    if (tf.includes('/') && !tf.endsWith('.test.ts')) {
+      // It's a directory path, add negation glob
+      return [tf, '!_auc-*/**/*.test.ts']
+    }
+    return tf
+  }).flat()
+  
+  const command = ["bun", "test", ...args]
   const spawnedProcess = Bun.spawn(command, {
     cwd: process.cwd(),
     stdin: "inherit",