feat(cabana): add the My account page with subtitle and password change

- lagoon: 202610090001_backend_users_metadata adds WinterCMS's nullable
  jsonable backend_users.metadata column (TEXT); rollback drops only it
- cabana.BackendUser.Metadata and Subtitle read metadata.subtitle leniently
  (NULL, blank, null, [], invalid JSON and non-strings read as empty)
- GET /auth/me returns subtitle; PUT /account edits the signed-in admin's
  own names, email and subtitle, and the password with current_password;
  any other key is a 422 and nothing is written
- email: required, valid, 6-255 chars, unique against other admins' email
  and login ignoring case (soft-deleted included); a unique-index race is 422
- a password change sets tokens_valid_after, revokes the presented token and
  gives a cookie session a fresh cookie
- swag annotation, regenerated admin.json and schema.d.ts; route inventories,
  CSRF walk (27) and OpenAPI conformance learn the route
- SPA: My account item in the user menu opens /account (AccountView), which
  saves through PUT /account and updates the top bar via setCurrentUser
- backend::lang.myaccount strings (en, pl), rebuilt boardwalk dist
- cabana and lagoon READMEs, users-and-permissions and admin-spa docs

docs/backend/admin-spa.md

@@ -33,6 +33,8 @@ A list row that carries a state (deleted, negative or disabled) shows a text bad
 
 A form whose schema carries `preview` has a read-only record screen at `<controller>/<id>/preview`, next to the list (`<controller>`), the create form (`<controller>/create`) and the update form (`<controller>/<id>`). It renders the fields whose context allows `preview` as text, the status hint partial above them and, in its footer, the record actions the record response offers before the one edit button. Opening that route for a form without a preview goes to the update form. See [Preview screen](forms.md#preview-screen).
 
+The user menu in the top bar has a My account item that opens `<prefix>/account`. That screen edits the signed-in administrator's own first name, last name, email and subtitle, shows the login read-only, and changes the password when a new one is typed together with the current one. Server validation errors show on their fields, and a successful save updates the name in the top bar without a reload. See [My account](users-and-permissions.md#my-account).
+
 ## Types from OpenAPI
 
 The admin API is described by swag annotations in cabana. `scripts/check-admin-openapi.sh` generates the OpenAPI document (`admin/openapi/admin.json`) from them and the SPA's TypeScript types (`admin/src/api/schema.d.ts`) from the document, so the SPA's API client is checked against the server's shapes at compile time. Type overrides for swag live in the root `.swaggo` (it documents `json.RawMessage` as an untyped value, which swag cannot resolve on its own). `--check` fails when either committed file is out of date: