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/ui/Button.vue

@@ -0,0 +1,42 @@
+<script setup lang="ts">
+import { computed, type Component } from 'vue'
+import { RouterLink, type RouteLocationRaw } from 'vue-router'
+
+// One button for the whole admin (design tokens): primary, outline, ghost and
+// danger (outline). With `to` it renders a router link styled the same way.
+const props = withDefaults(
+  defineProps<{
+    variant?: 'primary' | 'outline' | 'ghost' | 'danger'
+    size?: 'md' | 'sm'
+    type?: 'button' | 'submit'
+    disabled?: boolean
+    icon?: Component
+    to?: RouteLocationRaw
+  }>(),
+  { variant: 'outline', size: 'md', type: 'button', disabled: false, icon: undefined, to: undefined },
+)
+
+const variants: Record<NonNullable<typeof props.variant>, string> = {
+  primary: 'bg-primary text-on-primary hover:opacity-90',
+  outline: 'border border-border-strong bg-surface text-text hover:bg-hover',
+  ghost: 'text-muted hover:bg-hover hover:text-text',
+  danger: 'border border-danger bg-surface text-danger hover:bg-danger-soft',
+}
+
+const classes = computed(() => [
+  'inline-flex shrink-0 items-center justify-center gap-2 rounded-control px-4 font-semibold whitespace-nowrap no-underline transition-colors duration-150 ease-out disabled:cursor-not-allowed disabled:opacity-60',
+  props.size === 'sm' ? 'h-[38px]' : 'h-button',
+  variants[props.variant],
+])
+</script>
+
+<template>
+  <RouterLink v-if="to !== undefined" :to="to" :class="classes">
+    <component :is="icon" v-if="icon" :size="16" aria-hidden="true" />
+    <slot />
+  </RouterLink>
+  <button v-else :type="type" :disabled="disabled" :class="classes">
+    <component :is="icon" v-if="icon" :size="16" aria-hidden="true" />
+    <slot />
+  </button>
+</template>

admin/src/components/ui/Toast.vue

@@ -0,0 +1,36 @@
+<script setup lang="ts">
+import { Check, CircleAlert, X } from '@lucide/vue'
+import { t } from '../../app/i18n'
+import { dismissToast, toasts } from '../../state/useToasts'
+</script>
+
+<template>
+  <!-- Bottom centre, 88px up so it clears the sticky form footer. -->
+  <div class="pointer-events-none fixed inset-x-0 bottom-[88px] z-50 flex flex-col items-center gap-2 px-4">
+    <div
+      v-for="toast in toasts"
+      :key="toast.id"
+      :role="toast.tone === 'danger' ? 'alert' : 'status'"
+      :data-tone="toast.tone"
+      class="pointer-events-auto flex max-w-[560px] items-center gap-3 rounded-[14px] bg-[#1d2740] py-3 pr-2.5 pl-3.5 text-white shadow-toast"
+    >
+      <span
+        :class="toast.tone === 'danger' ? 'bg-[#f58a8a] text-[#1d2740]' : 'bg-accent text-on-accent'"
+        class="flex size-[26px] shrink-0 items-center justify-center rounded-full"
+        aria-hidden="true"
+      >
+        <CircleAlert v-if="toast.tone === 'danger'" :size="16" />
+        <Check v-else :size="16" />
+      </span>
+      <span class="font-medium">{{ toast.text }}</span>
+      <button
+        type="button"
+        :aria-label="t('backend::lang.form.close')"
+        class="flex size-8 items-center justify-center rounded-pager text-[#c3cbda] hover:bg-side-hover hover:text-white"
+        @click="dismissToast(toast.id)"
+      >
+        <X :size="16" aria-hidden="true" />
+      </button>
+    </div>
+  </div>
+</template>