feat(portal): add SSR operations and exclusive groups

design/us-009-velocity-admission.md

@@ -3,7 +3,7 @@ type: User Story
 title: Enforce registration at the Velocity proxy
 description: Online-mode Java connections are admitted only after a fail-closed account-manager decision.
 tags: [minecraft, velocity, whitelist, security]
-timestamp: 2026-08-01T22:34:31Z
+timestamp: 2026-08-01T23:10:59Z
 story_id: US-009
 status: verified
 ---
@@ -22,7 +22,7 @@ As a registered player, I want the Velocity proxy to recognize my approved Java
 - [x] Username fallback applies only when the stored account has no UUID.
 - [x] Successful fallback backfills UUID and canonical username.
 - [x] Changed usernames are persisted and audited.
-- [x] Registered players are allowed only when at least one assigned group has access enabled.
+- [x] Registered players are allowed only when their single effective group has access enabled; explicit assignments override the default group.
 - [x] Unknown players, group-disabled players, API failures, malformed responses, and unauthorized requests fail closed with registration guidance.
 - [x] The plugin records the real Velocity connection IP and supports Java Edition online mode only.