feat: announcement system upgrade + user management

- Add Source/TargetUserID fields to announcements, support individual push
- Add status (active/disabled) and DisabledReason to SysUser
- Add admin user management API (list, detail, enable/disable)
- Add login disabled check with reason prompt
- Add system-generated invitation notifications
- Allow invite reward amount configurable via system settings
- Frontend: AdminUsers page, update AdminAnnouncements with target user support

.gitignore

@@ -2,12 +2,17 @@
 backed/server
 backed/cpdaily-new
 backed/cpdaily-server
+backed/cmd/server/cpdaily-new
 backed/*.log
 backed/*.har
 
+# Frontend build (rebuilt by Docker multi-stage)
+backed/dist/
+frondend/dist/
+
 # Node
 frondend/node_modules/
-frondend/dist/
+frondend/*.tsbuildinfo
 
 # IDE
 .idea/