feat(10-03): tabs, toggles, relation fields, form lifecycle and settings pages

- FormTabs groups fields by tab (untabbed fields in the default tab) as a
  segmented tablist; a tab holding invalid fields after a 422 shows a
  count badge and the form switches to the first invalid field
- switch, checkbox and relation join the renderer registry: toggle cards
  (role=switch, 20px checkbox) keep a numeric value numeric; relation
  fields are read-only labels from meta.labels, a searchable single
  select over fields/{field}/options with emptyOption first, or ordered
  removable chips with an appending search (300 ms debounce, 20 per
  page, more on scroll or the more action)
- FormView gets the back button, record title and update subtitle, a
  sticky footer (Usuń with deleteConfirm then DELETE, Anuluj, Zapisz i
  zamknij to the mapped redirectClose, Zapisz), and asks before leaving a
  dirty form on any route change plus a beforeunload guard
- Settings: the rail pins Ustawienia to the bottom when /settings is
  non-empty; /settings lists pages by category; /settings/:code renders
  the settings schema through FormGrid and the registry, PUTs the values
  and maps a 422 like the record form
- New backend::lang keys (form.more_options, tab_default, discard,
  settings.back); form and settings smoke tests; boardwalk/dist rebuilt

admin/src/views/SettingsFormView.vue

@@ -0,0 +1,134 @@
+<script setup lang="ts">
+import { computed, nextTick, ref } from 'vue'
+import { useRoute } from 'vue-router'
+import { ArrowLeft } from '@lucide/vue'
+import { api } from '../api/client'
+import type { AdminRecord, FormView } from '../api/types'
+import { t } from '../app/i18n'
+import FormErrorBanner from '../components/form/FormErrorBanner.vue'
+import FormGrid from '../components/form/FormGrid.vue'
+import { contextAllows, editablePayload, fieldErrors, focusField } from '../components/form/formState'
+import Button from '../components/ui/Button.vue'
+import { settingsEntry } from '../state/useSettings'
+import { showToast } from '../state/useToasts'
+
+// One settings page (D-21) through the same FormGrid and field registry as
+// records: GET the schema and the values, PUT the values keyed by field name,
+// map a 422 the same way. Settings forms have no create step.
+const route = useRoute()
+const code = String(route.params.code ?? '')
+const ID_PREFIX = 'setting'
+
+const schema = ref<FormView | null>(null)
+const values = ref<AdminRecord>({})
+const errors = ref<Record<string, string[]>>({})
+const loading = ref(true)
+const failed = ref(false)
+const busy = ref(false)
+
+const fields = computed(() => (schema.value?.fields ?? []).filter((field) => contextAllows(field, 'update')))
+const fieldNames = computed(() => fields.value.map((field) => field.name))
+const title = computed(() => settingsEntry(code)?.label || schema.value?.name || code)
+const description = computed(() => settingsEntry(code)?.description ?? '')
+
+async function load(): Promise<void> {
+  const params = { path: { code } }
+  const [schemaResult, valuesResult] = await Promise.all([
+    api.GET('/settings/{code}/schema', { params }),
+    api.GET('/settings/{code}', { params }),
+  ])
+  schema.value = schemaResult.data?.data ?? null
+  values.value = { ...(valuesResult.data?.data.data ?? {}) }
+  failed.value = !schemaResult.data || !valuesResult.data
+  loading.value = false
+}
+
+function update(name: string, value: unknown): void {
+  values.value = { ...values.value, [name]: value }
+  if (errors.value[name]) {
+    const next = { ...errors.value }
+    delete next[name]
+    errors.value = next
+  }
+}
+
+async function onSave(): Promise<void> {
+  if (busy.value || !schema.value) {
+    return
+  }
+  busy.value = true
+  try {
+    const result = await api.PUT('/settings/{code}', {
+      params: { path: { code } },
+      body: editablePayload(fields.value, values.value),
+    })
+    if (result.data) {
+      errors.value = {}
+      values.value = { ...result.data.data.data }
+      showToast(t('backend::lang.settings.saved'))
+      return
+    }
+    if (result.response.status === 422) {
+      errors.value = fieldErrors(result.error?.error.details)
+      const first = fields.value.find((field) => errors.value[field.name])
+      await nextTick()
+      if (first) {
+        focusField(ID_PREFIX, first.name)
+      }
+      return
+    }
+    showToast(result.error?.error.message || t('backend::lang.form.error_generic'), 'danger')
+  } catch {
+    showToast(t('backend::lang.form.error_generic'), 'danger')
+  } finally {
+    busy.value = false
+  }
+}
+
+void load()
+</script>
+
+<template>
+  <section class="mx-auto flex w-full max-w-[980px] flex-col gap-5 pb-24">
+    <header class="flex items-center gap-4">
+      <Button
+        variant="outline"
+        data-action="back"
+        to="/settings"
+        :aria-label="t('backend::lang.settings.back')"
+        class="size-10! px-0!"
+      >
+        <ArrowLeft :size="18" aria-hidden="true" />
+      </Button>
+      <div class="flex min-w-0 flex-col">
+        <h1 class="truncate text-[24px] font-bold tracking-[-0.02em]">{{ title }}</h1>
+        <p v-if="description" class="text-muted">{{ description }}</p>
+      </div>
+    </header>
+
+    <p v-if="failed && !loading" role="alert" class="rounded-inner bg-danger-soft px-[18px] py-3.5 text-danger">
+      {{ t('backend::lang.form.load_failed') }}
+    </p>
+
+    <template v-else-if="schema">
+      <FormErrorBanner :errors="errors" :field-names="fieldNames" />
+      <form class="rounded-card border border-border bg-surface p-7 shadow-card" novalidate @submit.prevent="onSave">
+        <FormGrid
+          :fields="fields"
+          :values="values"
+          :errors="errors"
+          :source="null"
+          :id-prefix="ID_PREFIX"
+          @update="update"
+        />
+      </form>
+    </template>
+
+    <footer class="fixed inset-x-0 bottom-0 z-30 flex items-center justify-end gap-2.5 border-t border-border bg-surface px-8 py-3.5">
+      <Button variant="ghost" to="/settings">{{ t('backend::lang.form.cancel') }}</Button>
+      <Button variant="primary" data-action="save" :disabled="busy || loading || !schema" @click="onSave">
+        {{ busy ? t('backend::lang.form.saving') : t('backend::lang.form.save') }}
+      </Button>
+    </footer>
+  </section>
+</template>