Delete authored spec comments from the protocol server

Hive protocol server clients can now remove spec comments they authored, instead of having to switch to the dashboard for cleanup. The new delete_spec_comment tool accepts a comment identifier returned by existing spec tools, checks that the caller can view the parent spec, and enforces the same author-only rule already used for editing comments. The tool is registered as destructive in its protocol annotations, and non-authors receive the same unauthorized response used by comment updates.