feat(10-02): backend strings, controller messages and declarative toolbar

- phrasebook ships the backend::lang admin strings (pl, en) with CLDR
  plural maps, loads them as namespace backend, applies
  pact.HasLangOverrides trees (lang/<locale>/<namespace>/<group>.yaml)
  after every namespace, and fails activation when a backend key cannot
  convert to plural forms
- Translator.Forms, Bundle, Resolved and Has serve keys as CLDR form maps
- Public GET /lang returns every backend::lang key for the request
  locale over the fallback locale, Cache-Control no-cache
- config_list, config_form and config_relation accept a strict messages
  block; omitted keys take framework defaults, schemas serve every message
  as CLDR forms, and activation fails on a missing phrase key
- toolbar.buttons is an ordered [create, delete] list; the Winter string
  form, duplicates, unknown actions and delete without showCheckboxes fail
  at boot, and create is dropped when the controller has no form
- Form schema serves the raw Winter redirects; scaffold emits the list
  syntax; form and relation schema routes are typed in the admin OpenAPI

phrasebook/backend/lang/en/lang.yaml

@@ -0,0 +1,119 @@
+# Framework admin strings (D-20), resolved as backend::lang.<group>.<key>.
+# English equivalents of the Polish copy; plural texts are CLDR maps (one,
+# other), never pipe strings. Placeholders use :count, :name, :term (D-24).
+auth:
+  title: Welcome back
+  login: Login or email
+  password: Password
+  invalid: Invalid login details
+  submit: Sign in
+  logout: Sign out
+  session_expired: Your session has expired. Please sign in again.
+nav:
+  plugins: Plugins
+  sections: Sections
+  breadcrumbs: Breadcrumbs
+  empty: No sections are available.
+  settings: Settings
+  collapse: Collapse menu
+  expand: Expand menu
+  user_menu: User menu
+page:
+  not_found: Page not found.
+list:
+  search_prompt: Search…
+  no_records: There are no records in this view.
+  no_results: 0 results
+  loading: Loading…
+  load_failed: The list could not be loaded.
+  delete_selected: Delete selected
+  prev_page: Previous
+  next_page: Next
+  records_per_page: Per page
+  column_switch_true: "Yes"
+  column_switch_false: "No"
+  column_created: Created
+  column_updated: Updated
+  pagination_range: ":from–:to of :total"
+  results:
+    one: ":count result"
+    other: ":count results"
+  empty_value: "—"
+  clear_search: Clear search
+  select_all: Select all on this page
+  select_row: Select row
+  sort_ascending: Sort ascending
+  sort_descending: Sort descending
+form:
+  save: Save
+  save_and_close: Save and close
+  cancel: Cancel
+  delete: Delete
+  none: — none —
+  update: Edit
+  create: Create
+  return_to_list: Back to list
+  close: Close
+  confirm: Confirm
+  saving: Saving…
+  deleting: Deleting…
+  add: Add
+  remove_item: "Remove: :name"
+  add_item: Add…
+  select_placeholder: Select…
+  loading_options: Loading…
+  no_options: No results
+  unsupported_field: "Unsupported field type: :type"
+  error_title: Could not save.
+  error_fields:
+    one: "Fix :count field marked below."
+    other: "Fix :count fields marked below."
+  error_generic: The changes could not be saved. Please try again.
+  unsaved_confirm: You have unsaved changes. Discard them?
+  tab_errors:
+    one: ":count error"
+    other: ":count errors"
+relation:
+  add: Add
+  link: Link
+  unlink: Unlink
+  remove: Remove
+  search: Search…
+  add_count: "Add (:count)"
+  candidates_range: ":from–:to of :total"
+settings:
+  title: Settings
+  empty: No settings are available.
+  saved: Settings saved
+messages:
+  list:
+    record_count:
+      one: ":count record"
+      other: ":count records"
+    create: New record
+    empty_search: Nothing found
+    empty_search_hint: No record matches “:term”. Try another search.
+    selected: ":count selected"
+    delete_confirm: "Delete the selected (:count)?"
+    deleted:
+      one: "Deleted :count record"
+      other: "Deleted :count records"
+  form:
+    create: New record
+    update: Edit record
+    saved: Saved
+    delete_confirm: Delete this record?
+    deleted: Record deleted
+  relation:
+    link: Add
+    link_hint: Choose the records to link.
+    candidate_search: Search…
+    linked:
+      one: "Linked :count record"
+      other: "Linked :count records"
+    unlink_selected: Unlink selected
+    unlink_confirm: "Unlink the selected (:count)?"
+    unlinked:
+      one: "Unlinked :count record"
+      other: "Unlinked :count records"
+    empty: No linked records.