docs(spec): address the metadata item door by its singular type segment in the http-cache example

The seventh site of the card's slice, held back on the first pass because
packages/spec/src/api was inside a declared in-flight surface (#12522). That
claim has since closed (merged PR #13019), and the re-run check finds the
directory's only current claim (#13040) declared file-precisely at
endpoint-publish-gate.ts with 'Nothing else' -- disjoint from this file, and
its PR touches exactly that one file. No open PR touches http-cache.zod.ts.

Only the plural type segment moves. The /metadata prefix is a separate axis the
card does not scope, and the sibling example at :188 uses it too.

Part of #11042

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CPrUz21stTFhJRUirdc4yw

Author: claude

packages/spec/src/api/http-cache.zod.ts

@@ -105,7 +105,7 @@ export type ETagParsed = z.infer<typeof ETagSchema>;
  * Request with cache validation headers
  * 
  * @example
- * // GET /api/v1/metadata/objects/account
+ * // GET /api/v1/metadata/object/account
  * // Headers:
  * // If-None-Match: "686897696a7c876b7e"
  * // If-Modified-Since: Wed, 21 Oct 2015 07:28:00 GMT