What type of PR is this?

cleanup

What this PR does / why we need it:

This PR cleans up non-blocking CAMARA Validation warnings/hints in the ClickToDial OAS before the second r1.3 release candidate.

It addresses ClickToDial-owned OAS findings where the fix is local and does not change the API wire format:

• add an EventType enum schema for ClickToDial event types;
• rename ClickToDial-owned local schemas to PascalCase;
• add a conservative pattern for CallId;
• remove unused local wrapper schemas where common artifacts are referenced directly.

This follows the feedback in #94 to consider addressing the remaining warnings, including schema naming such as sink vs Sink.

Special notes for reviewers:

This PR intentionally does not modify:

• release-plan.yaml;
• code/common/*;
• CHANGELOG.md;
• README.md;
• .github/workflows/*.

The files under code/common/* are kept synced with Commonalities r4.2 via .sync-manifest.yaml and are not manually edited in this PR.

This PR does not execute /create-snapshot and does not start the release process.

Any remaining findings located in code/common/* should be handled centrally by Commonalities/tooling rather than locally in ClickToDial.

Changelog input

Clean up non-blocking OAS validation warnings without changing the API wire format.