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/release-evidence.ts

@@ -254,11 +254,14 @@ export async function appendReleaseEvidence(
       await handle.close();
     }
     await rename(temporary, absolute);
-    const directory = await open(parent, 'r');
-    try {
-      await directory.sync();
-    } finally {
-      await directory.close();
+    if (process.platform !== 'win32') {
+      // directory fsync only exists on POSIX
+      const directory = await open(parent, 'r');
+      try {
+        await directory.sync();
+      } finally {
+        await directory.close();
+      }
     }
     return Object.freeze(record);
   } finally {