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/FormGrid.vue

@@ -0,0 +1,48 @@
+<script setup lang="ts">
+import type { AdminRecord, ControllerParams, FormField as FormFieldSchema, RecordMeta } from '../../api/types'
+import FormField from './FormField.vue'
+
+// Two-column form grid (design screen 4): span left -> column 1, right ->
+// column 2, full (Winter's default) -> the whole row, auto and row -> the next
+// free slot. Below 600px everything is one column. Gaps are 22px x 24px.
+defineProps<{
+  fields: FormFieldSchema[]
+  values: AdminRecord
+  errors: Record<string, string[]>
+  labels?: RecordMeta['labels']
+  source?: ControllerParams | null
+  idPrefix?: string
+}>()
+const emit = defineEmits<{ update: [name: string, value: unknown] }>()
+
+function spanClass(span: string | undefined): string {
+  switch (span) {
+    case 'left':
+      return 'min-[600px]:col-start-1'
+    case 'right':
+      return 'min-[600px]:col-start-2'
+    case 'auto':
+    case 'row':
+      return ''
+    default:
+      return 'col-span-full'
+  }
+}
+</script>
+
+<template>
+  <div class="grid grid-cols-1 gap-x-6 gap-y-[22px] min-[600px]:grid-cols-2">
+    <FormField
+      v-for="field in fields"
+      :key="field.name"
+      :class="spanClass(field.span)"
+      :field="field"
+      :model-value="values[field.name]"
+      :errors="errors[field.name]"
+      :labels="labels?.[field.name]"
+      :source="source"
+      :id-prefix="idPrefix"
+      @update:model-value="(value: unknown) => emit('update', field.name, value)"
+    />
+  </div>
+</template>