Fix ToS consent enforcement — disable require_at_registration

Previously require_at_registration=true caused Cinny to silently complete
the m.login.terms UIA step during registration (~34ms), meaning users were
auto-consented without ever seeing the ToS page.

Setting require_at_registration=false removes the UIA step from registration.
New users start with NULL consent and are blocked by block_events_error on
first message send. Synapse sends a Server Notice DM with the /_matrix/consent
URL, which they must explicitly visit and submit before messaging is unblocked.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -438,6 +438,7 @@ Periodic `TLS/TCP socket error: Connection reset by peer` in coturn logs. Normal
 - [x] SSO/OIDC via Authelia
 - [x] `allow_existing_users: true` for linking accounts to SSO
 - [x] Password auth alongside SSO
+- [x] Terms of Service / consent enforcement — `require_at_registration: false`, `block_events_error` set; new users cannot send messages until they explicitly accept via `/_matrix/consent`; Synapse sends a Server Notice DM with the consent URL on first blocked send
 
 ### Webhooks & Integrations
 - [x] matrix-hookshot 7.3.2 — 11 active webhook services