docs(admin): add upgrade_to_34 release notes page

Assisted-by: Cursor:grok-4.7
Signed-off-by: whoalin1 <whoalin414@gmail.com>

Author: whoalin1

admin_manual/release_notes/index.rst

@@ -15,6 +15,7 @@ These sub pages will cover the most important changes in Nextcloud, as well as s
    :maxdepth: 1
 
    upgrade_to_35.rst
+   upgrade_to_34.rst
    upgrade_to_33.rst
    upgrade_to_32.rst
    upgrade_to_31.rst

admin_manual/release_notes/upgrade_to_34.rst

@@ -0,0 +1,22 @@
+=======================
+Upgrade to Nextcloud 34
+=======================
+
+Critical changes
+----------------
+
+There are **no additional critical upgrade steps** specific to Nextcloud 34
+beyond a normal major upgrade (backup, put the instance into maintenance mode,
+run ``occ upgrade``, then disable maintenance mode).
+
+Review the `official changelog <https://nextcloud.com/changelog/>`_ for feature
+and app changes in the Hub 26 Spring / Nextcloud 34 line, and confirm your
+stack still matches :doc:`../installation/system_requirements` before upgrading
+further to Nextcloud 35.
+
+System requirements
+-------------------
+
+Nextcloud 34 continues the PHP 8.3–8.5 support window used around this release
+line. Prefer staying on a currently supported PHP, database, and OS combination
+from the system requirements page when planning the upgrade.