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

modules/cabana/security_coverage_test.go

@@ -39,6 +39,7 @@ var phase09Routes = []adminRoute{
 	// refreshable token can be revoked) and is therefore not behind the guard.
 	{key: "POST /auth/logout", public: true},
 	{key: "GET /auth/me"},
+	{key: "PUT /account"},
 	{key: "GET /navigation"},
 	{key: "GET /settings"},
 	{key: "GET /settings/{code}/schema"},