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.record.json

@@ -6,7 +6,41 @@
     "size": "m",
     "weight": 12,
     "notes": "Round",
-    "color": "#0000ff"
+    "color": "#0000ff",
+    "active": true,
+    "featured": false,
+    "maker": 2,
+    "tags": [
+      3,
+      1
+    ],
+    "owner": 5,
+    "serial": "SN-1"
   },
-  "meta": { "labels": {} }
+  "meta": {
+    "labels": {
+      "maker": [
+        {
+          "value": 2,
+          "label": "Bolt & Co"
+        }
+      ],
+      "tags": [
+        {
+          "value": 3,
+          "label": "Round"
+        },
+        {
+          "value": 1,
+          "label": "Small"
+        }
+      ],
+      "owner": [
+        {
+          "value": 5,
+          "label": "dana@example.test"
+        }
+      ]
+    }
+  }
 }