fix: honor underscore-unused convention and make durability fsyncs cross-platform

- eslint: respect the repo's existing _-prefix convention for unused vars
- phase-one-blockers: derive projectRoot via import.meta.dirname so Windows
  checkouts stop producing C:\C:\... paths
- backup/release-evidence/cutover-orchestrator: skip POSIX-only directory
  fsync on win32 and fsync read-only handles through a writable handle

apps/api/src/cutover-orchestrator.ts

@@ -289,11 +289,14 @@ async function durableState(plan: CutoverPlan, state: CutoverState): Promise<voi
     await handle.close();
   }
   await rename(temporary, target);
-  const directory = await open(plan.stateDir, constants.O_RDONLY);
-  try {
-    await directory.sync();
-  } finally {
-    await directory.close();
+  if (process.platform !== 'win32') {
+    // directory fsync only exists on POSIX
+    const directory = await open(plan.stateDir, constants.O_RDONLY);
+    try {
+      await directory.sync();
+    } finally {
+      await directory.close();
+    }
   }
 }