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/dashboard_events.rs

@@ -52,7 +52,7 @@ pub enum DashboardEvent {
     /// enough to render the dashboard row without a `/api/state`
     /// refetch.
     ///
-    /// The approval's own kind (`"merge_config_pr"` / `"schedule_prompt"`) lives
+    /// The approval's own kind (`"schedule_prompt"` / `"update_meta_inputs"`) lives
     /// on `approval_kind` rather than `kind` because the latter is taken
     /// by the serde tag identifying which `DashboardEvent` variant
     /// this is.
@@ -61,15 +61,7 @@ pub enum DashboardEvent {
         id: i64,
         agent: String,
         approval_kind: &'static str,
-        sha_short: Option<String>,
         description: Option<String>,
-        /// Forge PR number, for `merge_config_pr` approvals only — lets
-        /// the live `applyApprovalAdded` path build the "review PR on
-        /// forge" link without waiting for a cold `/api/state` refresh
-        /// (mirrors `ApprovalView::pr_number`). `None` for every other
-        /// kind.
-        #[serde(skip_serializing_if = "Option::is_none")]
-        pr_number: Option<u64>,
     },
     /// A pending approval transitioned to a terminal state
     /// (approved / denied / failed). Clients move the row out of the
@@ -79,7 +71,6 @@ pub enum DashboardEvent {
         id: i64,
         agent: String,
         approval_kind: &'static str,
-        sha_short: Option<String>,
         /// `"approved"` / `"denied"` / `"failed"`.
         status: &'static str,
         resolved_at: DateTime<Utc>,
@@ -307,17 +298,14 @@ mod tests {
                 seq: 1,
                 id: 1,
                 agent: "x".into(),
-                approval_kind: "merge_config_pr",
-                sha_short: None,
+                approval_kind: "schedule_prompt",
                 description: None,
-                pr_number: None,
             },
             DashboardEvent::ApprovalResolved {
                 seq: 1,
                 id: 1,
                 agent: "x".into(),
-                approval_kind: "merge_config_pr",
-                sha_short: None,
+                approval_kind: "schedule_prompt",
                 status: "approved",
                 resolved_at: hive_sh4re::wire_time::from_secs(0),
                 note: None,