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/settings.json

@@ -0,0 +1,104 @@
+{
+  "list": {
+    "data": [
+      {
+        "code": "search",
+        "label": "Search",
+        "description": "Search engine options",
+        "icon": "search",
+        "category": "System",
+        "keywords": [],
+        "model": "Acme\\Demo\\Models\\Settings",
+        "order": 20
+      },
+      {
+        "code": "mail",
+        "label": "Mail",
+        "description": "Outgoing mail",
+        "icon": "icon-cog",
+        "category": "System",
+        "keywords": [],
+        "model": "Acme\\Demo\\Models\\MailSettings",
+        "order": 10
+      },
+      {
+        "code": "branding",
+        "label": "Branding",
+        "description": "Logo and colours",
+        "icon": "palette",
+        "category": "Appearance",
+        "keywords": [],
+        "model": "Acme\\Demo\\Models\\Branding",
+        "order": 5
+      }
+    ],
+    "meta": {
+      "locale": "en"
+    }
+  },
+  "schema": {
+    "data": {
+      "name": "Search",
+      "fields": [
+        {
+          "name": "use_engine",
+          "label": "Use the search engine",
+          "type": "switch",
+          "default": 0,
+          "comment": "Queries go to the external engine",
+          "required": true
+        },
+        {
+          "name": "engine_host",
+          "label": "Engine host",
+          "type": "text",
+          "span": "full"
+        }
+      ],
+      "messages": {
+        "create": {
+          "other": "New record"
+        },
+        "update": {
+          "other": "Edit record"
+        },
+        "saved": {
+          "other": "Saved"
+        },
+        "deleteConfirm": {
+          "other": "Delete?"
+        },
+        "deleted": {
+          "other": "Deleted"
+        }
+      },
+      "meta": {
+        "locale": "en"
+      },
+      "redirects": {
+        "create": {
+          "redirect": "",
+          "redirectClose": ""
+        },
+        "update": {
+          "redirect": "",
+          "redirectClose": ""
+        },
+        "default": ""
+      }
+    },
+    "meta": {
+      "locale": "en"
+    }
+  },
+  "values": {
+    "data": {
+      "data": {
+        "use_engine": 0,
+        "engine_host": "search.local"
+      },
+      "exists": true
+    },
+    "meta": {}
+  }
+}