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

cabana/admin_openapi.go

@@ -66,6 +66,12 @@ type ListEnvelope[T any] struct {
 // list or form schema (D-16).
 type AdminRecord map[string]any
 
+// AdminIDsRequest is the body of the id-list writes: bulk delete, relation
+// link and relation unlink.
+type AdminIDsRequest struct {
+	IDs []uint64 `json:"ids"`
+}
+
 // AdminLoginRequest is the admin login body. Either login or email
 // identifies the backend user.
 type AdminLoginRequest struct {
@@ -220,6 +226,7 @@ func AdminSettingsGet() {}
 // @Produce json
 // @Security BackendBearer
 // @Param code path string true "Settings code"
+// @Param body body AdminRecord true "Setting values keyed by field name"
 // @Success 200 {object} Envelope[SettingsResult]
 // @Failure 401 {object} ErrorEnvelope
 // @Failure 403 {object} ErrorEnvelope
@@ -331,6 +338,7 @@ func AdminFilterOptions() {}
 // @Param dir query string false "Sort direction (asc or desc)"
 // @Param page query integer false "Page"
 // @Param per_page query integer false "Records per page"
+// @Param filter query object false "Filter values keyed by filter name, sent as filter[<name>]=<value>"
 // @Success 200 {object} ListEnvelope[[]AdminRecord]
 // @Failure 401 {object} ErrorEnvelope
 // @Failure 403 {object} ErrorEnvelope
@@ -350,6 +358,7 @@ func AdminList() {}
 // @Param vendor path string true "Vendor"
 // @Param plugin path string true "Plugin"
 // @Param controller path string true "Controller"
+// @Param body body AdminRecord true "Field values keyed by field name; relation fields carry ids"
 // @Success 201 {object} RecordEnvelope
 // @Failure 401 {object} ErrorEnvelope
 // @Failure 403 {object} ErrorEnvelope
@@ -368,6 +377,7 @@ func AdminCreate() {}
 // @Param vendor path string true "Vendor"
 // @Param plugin path string true "Plugin"
 // @Param controller path string true "Controller"
+// @Param body body AdminIDsRequest true "Record ids"
 // @Success 200 {object} Envelope[BulkResult]
 // @Failure 401 {object} ErrorEnvelope
 // @Failure 403 {object} ErrorEnvelope
@@ -405,6 +415,7 @@ func AdminShow() {}
 // @Param plugin path string true "Plugin"
 // @Param controller path string true "Controller"
 // @Param id path integer true "Record id"
+// @Param body body AdminRecord true "Field values keyed by field name; relation fields carry ids"
 // @Success 200 {object} RecordEnvelope
 // @Failure 401 {object} ErrorEnvelope
 // @Failure 403 {object} ErrorEnvelope
@@ -481,6 +492,7 @@ func AdminRelationCandidates() {}
 // @Param controller path string true "Controller"
 // @Param id path integer true "Owner id"
 // @Param name path string true "Relation name"
+// @Param body body AdminIDsRequest true "Related record ids"
 // @Success 200 {object} Envelope[RelationMutationResult]
 // @Failure 401 {object} ErrorEnvelope
 // @Failure 403 {object} ErrorEnvelope
@@ -501,6 +513,7 @@ func AdminRelationLink() {}
 // @Param controller path string true "Controller"
 // @Param id path integer true "Owner id"
 // @Param name path string true "Relation name"
+// @Param body body AdminIDsRequest true "Related record ids"
 // @Success 200 {object} Envelope[RelationMutationResult]
 // @Failure 401 {object} ErrorEnvelope
 // @Failure 403 {object} ErrorEnvelope