docs(changeset): drop StandardSchemaV1 from new-exports list

It was already exported from core/public on main; this PR only adds
isSpecType, specTypeSchemas, SpecTypeName, and SpecTypes.

Author: felixweinberger

.changeset/spec-type-schema.md

@@ -3,4 +3,4 @@
 '@modelcontextprotocol/server': minor
 ---
 
-Export `isSpecType` and `specTypeSchemas` records for runtime validation of any MCP spec type by name. `isSpecType.ContentBlock(value)` is a type predicate; `specTypeSchemas.ContentBlock` is a `StandardSchemaV1<ContentBlock>` validator. Guards are standalone functions, so `arr.filter(isSpecType.ContentBlock)` works. Also export the `StandardSchemaV1`, `SpecTypeName`, and `SpecTypes` types.
+Export `isSpecType` and `specTypeSchemas` records for runtime validation of any MCP spec type by name. `isSpecType.ContentBlock(value)` is a type predicate; `specTypeSchemas.ContentBlock` is a `StandardSchemaV1<ContentBlock>` validator. Guards are standalone functions, so `arr.filter(isSpecType.ContentBlock)` works. Also export the `SpecTypeName` and `SpecTypes` types.