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/tests/fixtures/widgets.options.json

@@ -1,9 +1,85 @@
 {
   "maker": {
     "data": [
-      { "value": "1", "label": "Acme Works" },
-      { "value": "2", "label": "Bolt & Co" }
+      {
+        "value": "1",
+        "label": "Acme Works"
+      },
+      {
+        "value": "2",
+        "label": "Bolt & Co"
+      }
     ],
-    "meta": { "locale": "en" }
+    "meta": {
+      "locale": "en"
+    }
+  },
+  "makerField": {
+    "data": [
+      {
+        "value": 1,
+        "label": "Acme Works"
+      },
+      {
+        "value": 2,
+        "label": "Bolt & Co"
+      }
+    ],
+    "meta": {
+      "page": 1,
+      "per_page": 20,
+      "total": 3,
+      "last_page": 2
+    }
+  },
+  "makerFieldPage2": {
+    "data": [
+      {
+        "value": 7,
+        "label": "Cog Ltd"
+      }
+    ],
+    "meta": {
+      "page": 2,
+      "per_page": 20,
+      "total": 3,
+      "last_page": 2
+    }
+  },
+  "makerFieldSearch": {
+    "data": [
+      {
+        "value": 1,
+        "label": "Acme Works"
+      }
+    ],
+    "meta": {
+      "page": 1,
+      "per_page": 20,
+      "total": 1,
+      "last_page": 1
+    }
+  },
+  "tagsField": {
+    "data": [
+      {
+        "value": 1,
+        "label": "Small"
+      },
+      {
+        "value": 3,
+        "label": "Round"
+      },
+      {
+        "value": 4,
+        "label": "Large"
+      }
+    ],
+    "meta": {
+      "page": 1,
+      "per_page": 20,
+      "total": 3,
+      "last_page": 1
+    }
   }
 }