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/forge/repos.rs

@@ -907,7 +907,7 @@ async fn apply_operator_branch_protection(repo: &str, token: &str) -> Result<()>
 /// - **`main` is never directly pushable** — no push is enabled on the
 ///   protected branch, so neither the agent (a write collaborator) nor
 ///   hive-c0re can `git push` it. It only advances via the config-PR merge
-///   handler (`run_merge_config_pr`), which fast-forward-*merges* the reviewed
+///   node (`actions::run_deploy_apply`), which fast-forward-*merges* the reviewed
 ///   head through the forge merge API (`Do=fast-forward-only`,
 ///   `head_commit_id` pinned to the reviewed sha).
 /// - **merge is whitelisted to `core`** — only hive-c0re can merge a config PR;