add 25.12 and update fast channel start date

Author: Blargian

docs/cloud/reference/01_changelog/02_release_status.md

@@ -46,6 +46,19 @@ For advance testing before production upgrades, use the Fast or Regular channel
 :::
 
 <ReleaseSchedule releases={[
+    {
+     changelog_link: 'https://clickhouse.com/docs/changelogs/25.12',
+     version: '25.12',
+     fast_start_date: '2026-02-10',
+     fast_end_date: 'TBD',
+     regular_start_date: 'TBD',
+     regular_end_date: 'TBD',
+     slow_start_date: 'TBD',
+     slow_end_date: 'TBD',
+     fast_progress: 'green',
+     regular_progress: 'green',
+     slow_progress: 'green'
+   },
    {
      changelog_link: 'https://clickhouse.com/docs/changelogs/25.10',
      version: '25.10',