docs: X-Quota-Reset is a UTC date, not a timestamp (#97)

## Summary

The docs described `X-Quota-Reset` as an ISO-8601 timestamp
(`2026-06-01T00:00:00Z`). The API sends the UTC date the calendar-month
quota resets, `YYYY-MM-DD` (`api/src/lib/rate-limit.ts` builds it from
`nextMonth.toISOString().split('T')[0]`), and falls back to `never` only
when it has no reset date. The doc text and example now match. Found in
a docs audit across every repo, checked against the API source.

## Type of change

- [ ] Bug fix (no breaking change)
- [ ] New feature (no breaking change)
- [ ] Breaking change (existing callers must update)
- [x] Docs, tests, or internal maintenance only

## Public API

None. A doc comment or README example only; the field stays a string.

## Test plan

Docs only. The hooks ran lint and typecheck on commit and push.

## Checklist

- [x] Tests cover the new behavior, and the suite passes locally (no
behavior changed)
- [x] Lint, format, and type checks pass
- [x] Docs and README examples updated if the public surface changed
- [x] No secrets, credentials, or personal data in the diff or the tests

Author: vvillait88

src/types.ts

@@ -153,8 +153,8 @@ export interface QuotaInfo {
   limit: number | null;
   /** `X-Quota-Used`: current usage within the period. */
   used: number | null;
-  /** `X-Quota-Reset`: ISO-8601 timestamp when the period resets, or `'never'` for lifetime
-   *  caps. The API emits the literal string `'never'` for tiers without a reset. */
+  /** `X-Quota-Reset`: the UTC date (`YYYY-MM-DD`) the calendar-month quota resets, e.g.
+   *  `2026-06-01`, or `'never'` when the API has no reset date for the account. */
   reset: string | null;
 }