Annotations: missing type validation (RSAN1a3)

[paddybyers]

Spec point

• RSAN1a3: "The SDK must validate that the user supplied a `type`. All other fields are optional." Should throw error code 40003.

Observed behaviour

`constructValidateAnnotation()` does not validate that `type` is present. An annotation without a type is published without error, and the request succeeds (or fails server-side with a less informative error).

Failing test

Test	Expected	Actual
`RSAN1a3 - type required`	Throw with error code 40003	No error thrown

Reproduction

```bash
RUN_DEVIATIONS=1 npx mocha --grep "RSAN1a3" test/uts/rest/channel/annotations.test.ts
```

From PR #2191, branch `uts-rest`.

┆Issue is synchronized with this Jira Task by Unito