Fleet status badge reads "3 error" instead of "3 errors"

## What

The fleet status badge on the admin Overview reads "3 error" when three connections are failing. The word needs a plural.

## Where

`src/components/admin/tabs/OverviewTab.tsx` line 533:

```tsx

{errorCount} error

```

The sibling badge just above reads `{degradedCount} degraded`, which is an adjective and reads correctly at any count. This one is a noun and does not.

## Expected

The badge reads "1 error" for one and "3 errors" for three.

## How to fix

1. In `src/components/admin/tabs/OverviewTab.tsx` line 533, make the noun agree with the count: `{errorCount} error{errorCount === 1 ? "" : "s"}`.
2. Check the rest of the file for the same shape before you finish. If another badge or label pluralises a noun by hand, fix it the same way in this pull request.

## How to check

Run `bun run dev` and open the admin dashboard with connections in an error state. One failing connection should read "1 error", two or more should read "2 errors".

Open src/components/admin/tabs/OverviewTab.tsx at line 533 and inspect the error badge and nearby labels. Check the rest of the file for other hand-pluralised noun labels, then run bun run dev and open the admin dashboard with connections in an error state. Done means one failing connection reads "1 error" and multiple failing connections read "2 errors".

Written by the indexing model from the issue text.