feat: opt-in Cloudflare Turnstile on login and register (golem15.user.turnstile)

- empty (default) adds nothing; open or closed appends turnstile:{mode} to
  POST /login and /register only; any other value fails boot naming the key
- TestTurnstileRoutesSmoke records the declared routes with a recording router

README.md

@@ -205,6 +205,7 @@ Defaults live in `config/config.yaml` and are merged under `golem15.user.*`. Any
 | `golem15.user.password.min_length` | `8` | Minimum password length. |
 | `golem15.user.api_tokens.prefix` | `usr_` | Prefix for newly minted and accepted shared API-token secrets. Override an existing application's legacy prefix without creating a plugin-specific token table. |
 | `golem15.user.privileged_groups` | `[admin]` | Codes of the privileged user groups. Membership of such a group, the group's code and its delete, and the email, password and permanent delete of its members need `golem15.users.manage_privileged_groups`. Read on every request. An empty list protects no group. |
+| `golem15.user.turnstile` | `""` | Cloudflare Turnstile on `POST /login` and `POST /register`. Empty adds nothing; `open` or `closed` appends the framework's `turnstile:open` or `turnstile:closed` middleware to those two routes only (summercms v0.3.0 and later; secret in `turnstile.secret`, token in the `turnstile_token` field). `open` lets requests pass when Cloudflare is unreachable, `closed` refuses them. Any other value fails boot. |
 
 ## CLI commands