feat(boardwalk): expose the admin build id and show a reload banner when a new build is deployed (quick-261028-rqb)

- boardwalk.BuildID hashes the dist tree plus the binary's build info once
  per handler; X-Summer-Build on every response, {prefix}/build.json and the
  summer-admin-build meta carry it
- the SPA reads the booted build, re-checks on focus, visibility and every
  5 minutes, and shows UpdateBanner on a different build

modules/phrasebook/backend/lang/en/lang.yaml

@@ -543,3 +543,6 @@ permissions:
   manage_users_comment: "Create, edit, deactivate and delete administrator accounts."
   manage_roles: "Manage roles"
   manage_roles_comment: "Create and edit roles and the permissions they grant."
+version:
+  available: "A new version of the admin is available."
+  reload: "Reload"

modules/phrasebook/backend/lang/pl/lang.yaml

@@ -577,3 +577,6 @@ permissions:
   manage_users_comment: "Tworzenie, edycja, dezaktywacja i usuwanie kont administratorów."
   manage_roles: "Zarządzanie rolami"
   manage_roles_comment: "Tworzenie i edycja ról oraz uprawnień, które nadają."
+version:
+  available: "Dostępna jest nowa wersja panelu."
+  reload: "Odśwież"