fix(admin): resolve tunnel owner emails via one listUsers scan

The upstream admin gateway deterministically truncates the first per-row
getUserById that immediately follows a request's auth check, yielding an
empty body the per-call retry cannot clear — so a couple of tunnel rows
showed owner_email '—' on every load regardless of retry or concurrency.
Replace the per-row getUserById fan-out with a single bounded listUsers
scan (same transient retry) that builds an id->email map and stops early
once every owner on the page is resolved. A single listUsers read does not
hit the truncation pattern, eliminating the dashes. Remove the now-unused
mapWithConcurrency helper and OWNER_EMAIL_CONCURRENCY constant.

lib/admin/retry.ts

@@ -126,33 +126,3 @@ export async function withAdminRetry<R extends { error: MaybeError }>(
   if (threw) throw lastThrown;
   return lastResult as R;
 }
-
-/**
- * Map over `items` running at most `concurrency` async tasks at a time, while
- * preserving result order.
- *
- * Firing every GoTrue admin lookup at once (e.g. one `getUserById` per tunnel
- * row) can self-inflict an upstream throttle: the proxy truncates the tail of a
- * large concurrent burst, producing the very empty-body responses we retry on —
- * and because the retries fire back into the same saturated window, a few rows
- * can still fail. Bounding the concurrency keeps each lookup inside the
- * throttle's allowance so {@link withAdminRetry} reliably resolves every row.
- */
-export async function mapWithConcurrency<T, R>(
-  items: readonly T[],
-  concurrency: number,
-  task: (item: T, index: number) => Promise<R>,
-): Promise<R[]> {
-  const results = new Array<R>(items.length);
-  const limit = Math.max(1, Math.min(concurrency, items.length || 1));
-  let next = 0;
-  async function worker(): Promise<void> {
-    for (;;) {
-      const i = next++;
-      if (i >= items.length) return;
-      results[i] = await task(items[i], i);
-    }
-  }
-  await Promise.all(Array.from({ length: limit }, () => worker()));
-  return results;
-}