docs: define PR acceptance and release process

.github/pull_request_template.md

@@ -16,6 +16,9 @@
 
 Exact head SHA: `TBD`
 
+Review and acceptance are bound to this SHA. Pushing another commit invalidates the
+record below until it is updated and the new head is green.
+
 | Check | Result | Evidence or notes |
 |---|---|---|
 | Focused regression/contract tests | TBD | |
@@ -54,7 +57,13 @@ Use `Not applicable` when this pull request makes no research or performance cla
 - [ ] Research and performance claims are traceable to exact-head evidence and scoped to what was tested.
 - [ ] Every commit has a verifiable signature from its actual author or approved integration identity.
 - [ ] The branch has not been force-pushed and the exact head is ready for review.
+- [ ] I understand that green PR checks establish review readiness; maintainer
+      acceptance, canonical merge verification, and release certification are
+      separate gates.
 
 A green PR gate makes the submission reviewable. Maintainers may add further tests
 or hardening in separately attributable commits before merge; behavior changes with
 zero relevant coverage remain blocked.
+
+See [`docs/RELEASE_PROCESS.md`](../docs/RELEASE_PROCESS.md) for the exact-head
+acceptance, merge, tag, snapshot, and publication process.