feat(10-03): open, edit and save a record with toast and 422 feedback

- The SPA loads the backend::lang bundle before /auth/me, sets the
  document language from meta.locale and renders plural messages with
  Intl.PluralRules; interpolate mirrors phrasebook for :name/:Name/:NAME
- Create and record routes; mapWinterUrl maps recordUrl and redirects
  onto the controller's list, create and record routes only
- List rows open their record; FormView loads the form schema and the
  record, shows context-allowed fields in the span grid, saves values
  keyed by field name and toasts the resolved saved message
- A 422 puts each message under its field (aria-invalid,
  aria-describedby), shows the plural banner, focuses the first invalid
  field in schema order and clears a field's error on change
- The D-05 registry maps text, textarea, number and dropdown; any other
  type renders the unsupported-field box with the type in DM Mono
- The admin OpenAPI document declares the write request bodies
  (AdminRecord, AdminIDsRequest) and the list filter query as a
  deepObject, so the typed client can send them
- New backend::lang form.load_failed key; boardwalk/dist rebuilt

admin/src/components/shell/AppShell.vue

@@ -4,6 +4,7 @@ import { useRoute } from 'vue-router'
 import { ChevronRight } from '@lucide/vue'
 import PluginRail from './PluginRail.vue'
 import SectionPanel from './SectionPanel.vue'
+import Toast from '../ui/Toast.vue'
 import { t } from '../../app/i18n'
 import { controllerIdFromPath } from '../../app/controllerRoutes'
 import { currentUser } from '../../state/useAuth'
@@ -68,5 +69,6 @@ const initials = computed(() =>
         <slot />
       </main>
     </div>
+    <Toast />
   </div>
 </template>