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/form/FieldRenderer.vue

@@ -0,0 +1,25 @@
+<script setup lang="ts">
+import { computed } from 'vue'
+import { rendererFor, type FieldControlProps } from './registry'
+
+// Picks the control for field.type from the registry (D-05) and forwards the
+// shared control props and the value update.
+const props = defineProps<FieldControlProps>()
+const emit = defineEmits<{ 'update:modelValue': [value: unknown] }>()
+
+const control = computed(() => rendererFor(props.field.type))
+</script>
+
+<template>
+  <component
+    :is="control"
+    :field="field"
+    :model-value="modelValue"
+    :control-id="controlId"
+    :invalid="invalid"
+    :described-by="describedBy"
+    :labels="labels"
+    :source="source"
+    @update:model-value="(value: unknown) => emit('update:modelValue', value)"
+  />
+</template>