docs: describe the deploy subtree

Rewrite the approval flow's step 4 as the three phases, with the reason
the rollback state is a git ref, and refresh the coordinator's node
inventory + dispatch table. Fix four doc comments that still pointed at
the deleted `run_merge_config_pr`.

hive-c0re/src/lifecycle/setup.rs

@@ -71,7 +71,7 @@ async fn ensure_applied_remote(proposed_dir: &Path, name: &str) -> Result<()> {
 /// proposed's initial commit in via `git fetch`, tag it `deployed/0`.
 /// This is the *only* time hive-c0re reads from `proposed` for an
 /// agent — subsequent config changes are fetched from the reviewed
-/// forge PR head at merge time (see `actions::run_merge_config_pr`).
+/// forge PR head at merge time (see `actions::run_deploy_apply`).
 ///
 /// `proposed_dir` is `None` on rebuild paths where the repo already
 /// exists — we just verify it's the right shape and bail otherwise.