chore(release): bump MTA version 1.11.4 → 1.12.0 for PROD

[jung-thomas]

Minor version bump ahead of the blue-green PROD deploy of today's main delta.

Why minor: main carries features since PROD's current 1.11.4 (gitSha af65aa4c):

• devtoberfest home intro copy + rotating arcade ticker (feat(devtoberfest): welcome intro copy + rotating arcade ticker on home #1521)
• petoberfest slideshow polish + admin Delete + guarded purge (fix(petoberfest): enable multi-select on moderation List Report (approve no-op + mass-approve) #1507–feat(petoberfest): framed slideshow with pause/nav + admin permanent-delete #1511)
• CDN cache-header fix for dynamic data feeds (fix: prevent Akamai CDN caching of dynamic data feeds #1510)
• ANS fetch/raise hard timeout (fix(alerting): hard timeout on ANS raise — admin test alert fails fast instead of 502 #1505, chore(alerts): consume cds-alert-notification 1.0.2 (ANS fetch timeout) #1506)

Per the repo rule patch-for-fixes / minor-for-features, this is a minor bump. Only .deploy/mta.yaml is touched (root mta.yaml is legacy).

Deploy will run npm run deploy -- --env prod --strategy blue-green from fresh main after merge.