feat(v13.1): add documentation about the v13.1 release

Co-authored-by: Guillaume Viger <fenekku@users.noreply.github.com>

Author: max-moser

docs/releases/v13/version-v13.1.0.md

@@ -0,0 +1,81 @@
+# InvenioRDM v13.1
+
+*2026-03-19*
+
+We are happy to announce the release of InvenioRDM v13.1. This is a minor release which will become the maintained tip of v13.
+Future patches for v13 will land on this minor version only.
+
+
+## What's new?
+
+InvenioRDM v13.1 primarily backports the [request reviewers feature](/maintenance/architecture/requests/#reviewers-in-requests) to InvenioRDM v13.
+
+This feature allows the selection of users (or groups) as "reviewers" for requests.
+The selected reviewers will gain access to the request and its timeline (i.e. associated events and comments), and be able to comment on the request too.
+
+!!! warning "Enabling the feature requires reindexing the requests"
+    The information about the set of reviewers is stored in a new field in the request itself, so the schema has changed.
+    Enabling the feature will require the search mappings to be updated, and the requests to be reindexed.
+    For more details, see the [upgrade section below](#upgrading-from-v130-to-v131).
+
+
+### Selecting reviewers for requests
+
+The new request reviewers feature is (currently) opt-in, so you'll have to enable the `REQUESTS_REVIEWERS_ENABLED` feature flag via the configuration.
+Additionally, the behavior can be tweaked with a few more configuration items:
+
+```python
+REQUESTS_REVIEWERS_ENABLED = True
+"""Enable the request reviewers feature."""
+
+REQUESTS_REVIEWERS_MAX_NUMBER = 15
+"""Maximum number of reviewers allowed for a request."""
+
+USERS_RESOURCES_GROUPS_ENABLED = True
+"""Config to enable features related to existence of groups.
+
+Makes groups available for selection as request reviewers, in addition to users.
+"""
+```
+
+**Note** that the feature flag currently enables the request reviewers feature for *all kinds of requests*.
+
+
+### Other notable changes
+
+Even though the upgrade pulls in a number of major version bumps, there are actually only relatively few large changes.
+Most of the major releases there just bump their own dependencies (to better isolate from breaking changes) rather than introducing breaking changes themselves.
+
+Here are the most noteworthy changes:
+
+* [`Invenio-Users-Resources` v9.0.0](https://pypi.org/project/invenio-users-resources/9.0.3/): Tightened permissions for users endpoints in the REST API, and change of HTTP status code from `403` to `404` on permission errors for increased privacy
+* [`Invenio-RDM-Records` v20.2.0](https://pypi.org/project/invenio-rdm-records/20.2.0/): Renaming of several `React-Overridable` IDs; the full list of changed IDs is available in the [changelog for v20.2.0](https://github.com/inveniosoftware/invenio-rdm-records/blob/v20.2.0/CHANGES.rst?plain=1)
+
+
+
+## Upgrading from v13.0 to v13.1
+
+The first step of the upgrade process is of course to install the new packages.  
+To do so, make sure that the version specifiers for the Invenio-App-RDM dependency in your project definition (`pyproject.toml`, `Pipfile`, ...) allow for the `13.1.x` range of releases, e.g. `invenio-app-rdm[opensearch2]~=13.1.0`.
+
+The new packages should be found and installed via `invenio-cli install`.  
+If the v13.1 release of Invenio-App-RDM still doesn't get pulled in, remove your lock file (`uv.lock`, `Pipfile.lock`, ...) and try again.
+
+After installing the new packages, you'll need to update the search mappings for the requests index, and reindex all requests.
+
+```bash
+# update the search mappings for requests to include reviewers
+invenio index update requests-request-v1.0.0 --no-check
+
+# start bulk reindexing for all requests
+invenio rdm rebuild-all-indices --order requests
+```
+
+That's it.
+Other search indices like request events aren't affected and don't need to be updated.
+
+!!! info "No action needed if you don't want to use the feature"
+    If you *do not* intend to enable the request reviewers feature, no further action is necessary after upgrading the installed packages.
+    But updating the mappings won't hurt either.
+
+Enjoy v13.1! 😎

mkdocs.yml

@@ -214,6 +214,7 @@ nav:
       - Upgrade policy: releases/upgrade-policy.md
       - Security policy: releases/security-policy.md
       - Version v13:
+          - Release Notes v13.1: releases/v13/version-v13.1.0.md
           - Release Notes v13.0: releases/v13/version-v13.0.0.md
           - Upgrade from v12 to v13: releases/v13/upgrade-v13.0.md
       - Version v12: