feat: add Activity type system, DB migration, and self-only showActivity in sanitizeUser

- Add Activity, ActivityType, ActivityTimestamps, ActivityAssets types to shared types
- Add activity_update client event and activities field on presence_update server event
- Add userActivities to ready payload and showActivity to User/UpdateUserRequest
- Create shared activities.ts with ACTIVITY_LIMITS, ACTIVITY_PRIORITY, getPrimaryActivity
- Add show_activity column to users table (schema + migration)
- Update sanitizeUser with isSelf parameter; only include showActivity for self
- Fix .map(sanitizeUser) calls to use arrow wrapper to prevent index-as-boolean bug
- Mark auth routes (register/login) as isSelf=true since they return own user data

packages/server/src/routes/social.ts

@@ -502,6 +502,6 @@ export async function socialRoutes(app: FastifyInstance): Promise<void> {
       .limit(10)
       .all();
 
-    return reply.code(200).send(users.map(sanitizeUser));
+    return reply.code(200).send(users.map(u => sanitizeUser(u)));
   });
 }