docs: trim spec frontmatter to known fields (title only)

Official extension specs (ext-auth) use only `title:` in frontmatter
plus an <Info> protocol-revision marker. Remove the invented
extension_identifier / status / maintainers / related / profile_of
fields and restate the identifier and profile relationship in the body
prose where they belong.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

specification/draft/trust-annotations.mdx

@@ -1,15 +1,11 @@
 ---
 title: Trust Annotations
-extension_identifier: io.modelcontextprotocol/trust-annotations
-status: Draft (experimental)
-maintainers:
-  - "@SamMorrowDrums"
-  - "@rreichel3"
-related:
-  - https://github.com/modelcontextprotocol/modelcontextprotocol/pull/1913
-  - https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/seps/2133-extensions.md
 ---
 
+<Info>**Protocol Revision**: draft</Info>
+
+**Extension identifier:** `io.modelcontextprotocol/trust-annotations`
+
 > ⚠️ **Experimental draft skeleton.** This document captures the agreed shape
 > and the open questions. Normative text is intentionally thin pending
 > reference-implementation validation. Substantive discussion happens on PRs