SD-M2d: the checker's tag-wanted names the pull request's branch

The lead's ruling of 13:0x: the builder removes the tag when the branch ends, so it needs the branch.

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

ts/src/mesh-delivery-checker.ts

@@ -91,6 +91,8 @@ export interface VerdictHolderEvent {
 
 /** is the body of the holder's event tag-wanted. */
 export interface TagWantedHolderEvent {
+  /** the pull request's branch: its tag is removed when the branch ends */
+  "branch": string;
   /** its head */
   "head": string;
   /** the group member */