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/shared/package.json

@@ -8,7 +8,9 @@
   "exports": {
     ".": "./src/types.ts",
     "./src/permissions": "./src/permissions.ts",
-    "./src/permissions.js": "./src/permissions.ts"
+    "./src/permissions.js": "./src/permissions.ts",
+    "./src/activities": "./src/activities.ts",
+    "./src/activities.js": "./src/activities.ts"
   },
   "scripts": {
     "build": "tsc",