Add GITADORA rival support

Implement rival registration, profile responses, and Web UI controls.

The UI is functional only; visual design and polish are not included in this change.

gitadora@asphyxia/models/rival.ts

@@ -0,0 +1,8 @@
+export interface Rival {
+  collection: 'rival';
+
+  game: 'gf' | 'dm';
+  version: string;
+  rival_refid: string;
+  slot: number;
+}