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/FormErrorBanner.vue

@@ -0,0 +1,35 @@
+<script setup lang="ts">
+import { computed } from 'vue'
+import { CircleAlert } from '@lucide/vue'
+import { t, tc } from '../../app/i18n'
+
+// 422 banner (design screen 4): "Nie udało się zapisać. Popraw N pola…".
+// Messages of keys that are not form fields are listed here, so no server
+// message is lost.
+const props = defineProps<{ errors: Record<string, string[]>; fieldNames: string[] }>()
+
+const count = computed(() => Object.keys(props.errors).length)
+const orphans = computed(() =>
+  Object.entries(props.errors)
+    .filter(([name]) => !props.fieldNames.includes(name))
+    .flatMap(([, messages]) => messages),
+)
+</script>
+
+<template>
+  <div
+    v-if="count > 0"
+    role="alert"
+    data-error-banner
+    class="flex items-start gap-3 rounded-inner bg-danger-soft px-[18px] py-3.5 text-danger"
+  >
+    <CircleAlert :size="20" class="mt-px shrink-0" aria-hidden="true" />
+    <div class="flex flex-col gap-1">
+      <p>
+        <strong>{{ t('backend::lang.form.error_title') }}</strong>
+        {{ tc('backend::lang.form.error_fields', count) }}
+      </p>
+      <p v-for="(text, index) in orphans" :key="index" class="text-[13px]">{{ text }}</p>
+    </div>
+  </div>
+</template>