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.form-schema.json

@@ -0,0 +1,38 @@
+{
+  "data": {
+    "name": "Widget",
+    "fields": [
+      { "name": "name", "label": "Name", "type": "text", "span": "left", "required": true },
+      { "name": "code", "label": "Code", "type": "text", "span": "right", "comment": "Unique widget code" },
+      {
+        "name": "size",
+        "label": "Size",
+        "type": "dropdown",
+        "span": "left",
+        "emptyOption": "— none —",
+        "options": [
+          { "value": "s", "label": "Small" },
+          { "value": "m", "label": "Medium" },
+          { "value": "l", "label": "Large" }
+        ]
+      },
+      { "name": "weight", "label": "Weight", "type": "number", "span": "right" },
+      { "name": "notes", "label": "Notes", "type": "textarea", "span": "full", "size": "small" },
+      { "name": "color", "label": "Colour", "type": "colorpicker", "span": "left" }
+    ],
+    "messages": {
+      "create": { "other": "New widget" },
+      "update": { "other": "Editing widget" },
+      "saved": { "other": "Widget „:name” saved" },
+      "deleteConfirm": { "other": "Delete this widget?" },
+      "deleted": { "other": "Widget deleted" }
+    },
+    "meta": { "locale": "en" },
+    "redirects": {
+      "create": { "redirect": "acme/demo/widgets/update/:id", "redirectClose": "acme/demo/widgets" },
+      "update": { "redirect": "acme/demo/widgets", "redirectClose": "acme/demo/widgets" },
+      "default": "acme/demo/widgets"
+    }
+  },
+  "meta": { "locale": "en" }
+}