hive-c0re: a refused rev is an error log + Grafana alert, not a PR comment

A deploy request whose rev hive-c0re refuses (fetch failed, or the rev
does not descend from applied/main) no longer tries to comment on the PR
that merged it. Off the forge host that attempt always failed with "forge
core token absent". The refusal now logs at ERROR, message unchanged, and
the new `hh-config-rev-refused` Grafana rule fires on it.

Deleted with the posting: actions::post_rev_deploy_failure_to_pr, the
whole forge/pr_comment.rs (config_repo, merged_pr_for_commit,
post_pr_comment), and ReaderToken::value, whose only caller was
merged_pr_for_commit.

Refs #4851

docs/integrations/forge.md

@@ -77,12 +77,8 @@ forge container:
 - reseeding a purged `applied` repo, and the meta-update cascade's
   fast-forward of `applied/main`
 - seeding `proposed` from `agent-configs/<agent>` on first deploy
-- finding the PR that merged a config commit the hive refused to deploy
 - cloning and pulling `/knowledge`
 
-Posting the refusal as a comment on that PR still needs the `core` token, so
-only the forge host posts it.
-
 Roll a change to any of this out store host first (its granter writes the
 controller's grant on `swarm/hives/+/forge/token`), then the controller host,
 then the hives. A hive that starts before its token exists reads with the