config PRs: remove the hive's config-PR webhook, poll and core merge

An operator's merge on the forge deploys a config PR through
swarm-controller's DeployRequest{rev}. The hive-side path that queued a
MergeConfigPr approval and merged the PR as `core` goes:

- the `/webhook/config-pr` receiver, its HMAC secret, the WebhookRegister
  boot node and the org-hook registration; the hive vhost's `/webhook/`
  location
- the 5-minute config-PR poll
- ApprovalKind::MergeConfigPr, its dashboard card, and the deploy DAG it
  drove (DeployWindow, MergeVerify, DeployApply, FinalizeDeploy,
  DeployTail), with verify_commit, the two-phase meta deploy, rollback
  refs, the PR-failure comment and forge/pr_merge.rs
- `fetched_sha`, `sha_short`/`pr_number` on approval events, and
  `sha`/`tag` on HelperEvent::ApprovalResolved: only the merge path set
  them

`config_repo`, `merged_pr_for_commit` and `post_pr_comment` move to
forge/pr_comment.rs for the merged-rev deploy's refusal comment.
Approvals v5 drops stored `merge_config_pr` rows; a test reopens a v4
database holding them.

Closes #4850

hive-c0re/src/socket_server/mod.rs

@@ -21,14 +21,10 @@ use tokio::task::JoinHandle;
 
 use crate::coordinator::Coordinator;
 
-mod config_approvals;
 mod schedules;
 
-pub(crate) use config_approvals::submit_merge_config_pr;
 pub(crate) use schedules::filter_ghost_schedule_targets;
 pub use schedules::schedule_to_wire_public;
-#[cfg(test)]
-pub(crate) use schedules::tests::coordinator;
 
 use schedules::{
     EditSchedulePatch, handle_cancel_schedule, handle_edit_schedule, handle_fire_schedule_now,
@@ -735,15 +731,10 @@ fn handle_cancel_loose_end(
                 .mark_cancelled(id, canceller)
                 .map_err(|e| format!("{e:#}"))?;
             tracing::info!(%id, %canceller, agent = %approval.agent, "approval cancelled");
-            let sha_short = approval
-                .fetched_sha
-                .as_deref()
-                .map(|s| s[..s.len().min(12)].to_owned());
             coord.emit_approval_resolved(crate::coordinator::ApprovalResolved {
                 id: approval.id,
                 agent: approval.agent.as_str(),
                 approval_kind: <&str>::from(approval.kind),
-                sha_short,
                 status: "cancelled",
                 note: approval.note,
                 description: approval.description,