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/db/schema.ts

@@ -20,6 +20,7 @@ export const users = sqliteTable('users', {
   discoverable: integer('discoverable').default(1),
   profileUpdatedAt: integer('profile_updated_at'),
   passwordChangedAt: integer('password_changed_at'),
+  showActivity: integer('show_activity').notNull().default(1),
   createdAt: integer('created_at').notNull(),
 });