feat(10-03): open, edit and save a record with toast and 422 feedback

- The SPA loads the backend::lang bundle before /auth/me, sets the
  document language from meta.locale and renders plural messages with
  Intl.PluralRules; interpolate mirrors phrasebook for :name/:Name/:NAME
- Create and record routes; mapWinterUrl maps recordUrl and redirects
  onto the controller's list, create and record routes only
- List rows open their record; FormView loads the form schema and the
  record, shows context-allowed fields in the span grid, saves values
  keyed by field name and toasts the resolved saved message
- A 422 puts each message under its field (aria-invalid,
  aria-describedby), shows the plural banner, focuses the first invalid
  field in schema order and clears a field's error on change
- The D-05 registry maps text, textarea, number and dropdown; any other
  type renders the unsupported-field box with the type in DM Mono
- The admin OpenAPI document declares the write request bodies
  (AdminRecord, AdminIDsRequest) and the list filter query as a
  deepObject, so the typed client can send them
- New backend::lang form.load_failed key; boardwalk/dist rebuilt

admin/tests/fixtures/widgets.list-schema.json

@@ -8,15 +8,38 @@
     "showCheckboxes": true,
     "showSorting": true,
     "searchTerm": "",
-    "toolbarButtons": ["create"],
+    "toolbarButtons": [
+      "create"
+    ],
     "columns": [
-      { "key": "name", "label": "Name", "searchable": true, "sortable": true },
-      { "key": "code", "label": "Code", "searchable": true, "sortable": true },
-      { "key": "tags", "label": "Tags", "searchable": false, "sortable": false, "type": "relation", "relation": "tags", "select": "name" }
+      {
+        "key": "name",
+        "label": "Name",
+        "searchable": true,
+        "sortable": true
+      },
+      {
+        "key": "code",
+        "label": "Code",
+        "searchable": true,
+        "sortable": true
+      },
+      {
+        "key": "tags",
+        "label": "Tags",
+        "searchable": false,
+        "sortable": false,
+        "type": "relation",
+        "relation": "tags",
+        "select": "name"
+      }
     ],
     "filters": [],
     "rowActions": [],
-    "bulkActions": []
+    "bulkActions": [],
+    "recordUrl": "acme/demo/widgets/update/:id"
   },
-  "meta": { "locale": "en" }
+  "meta": {
+    "locale": "en"
+  }
 }