Add a change password feature using Better Auth's built-in
changePassword endpoint. On web, a dialog opens from a new card in the
Account section. On mobile, a dedicated screen is pushed from a new
SettingsRow. Both use listAccounts to detect credential-based accounts
and only show the option when the user has a password and password login
is enabled (respecting OIDC-only configurations).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>