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/components/form/fields/SwitchField.vue

@@ -0,0 +1,47 @@
+<script setup lang="ts">
+import { computed } from 'vue'
+import { toggleOn, toggleValue, type FieldControlProps } from '../registry'
+
+// Toggle card (design screen 4): the label as title, the comment as helper
+// text and a 44x26 role="switch" control; the off track uses borderStrong.
+const props = defineProps<FieldControlProps>()
+const emit = defineEmits<{ 'update:modelValue': [value: boolean | number] }>()
+
+const on = computed(() => toggleOn(props.modelValue))
+
+function toggle(): void {
+  emit('update:modelValue', toggleValue(props.modelValue, !on.value))
+}
+</script>
+
+<template>
+  <div
+    :class="invalid ? 'border-danger' : 'border-border'"
+    class="flex items-center justify-between gap-4 rounded-inner border px-4 py-3.5"
+    data-toggle-card
+  >
+    <div class="flex min-w-0 flex-col">
+      <label :for="controlId" class="font-semibold">
+        {{ field.label || field.name }}<span v-if="field.required" class="text-danger" aria-hidden="true"> *</span>
+      </label>
+      <p v-if="field.comment" :id="`${controlId}-comment`" class="text-[13px] text-muted">{{ field.comment }}</p>
+    </div>
+    <button
+      :id="controlId"
+      type="button"
+      role="switch"
+      :aria-checked="on ? 'true' : 'false'"
+      :aria-invalid="invalid ? 'true' : undefined"
+      :aria-describedby="describedBy || undefined"
+      :class="on ? 'bg-primary' : 'bg-border-strong'"
+      class="relative h-[26px] w-11 shrink-0 rounded-pill transition-colors duration-150 ease-out"
+      @click="toggle"
+    >
+      <span
+        :class="on ? 'translate-x-[18px] bg-on-primary' : 'translate-x-0 bg-white'"
+        class="absolute top-[3px] left-[3px] size-5 rounded-full shadow-tab transition-transform duration-150 ease-out"
+        aria-hidden="true"
+      />
+    </button>
+  </div>
+</template>