chore: restructure into monorepo and add open-source documentation

- Rename helix-server -> server and helix-web -> web
- Remove helix-api (bruno collection and docs site)
- Merge per-module .gitignore files into the root .gitignore
- Add README, AGENTS, CONTRIBUTING and MIT LICENCE
- Add full-stack docker-compose (postgres, redis, server, web via Caddy)
  with web Dockerfile, Caddyfile and Compose server config
- Keep the Gradle wrapper jar tracked after the .gitignore merge
- Copy gradle.properties into the server Docker build image

web/src/config/dayjs-config/index.ts

@@ -0,0 +1,11 @@
+// 配置插件
+import dayjs from "dayjs"
+
+import duration from "dayjs/plugin/duration"
+dayjs.extend(duration)
+
+// 配置语言
+import "dayjs/locale/zh-cn"
+dayjs.locale("zh-cn")
+
+console.log("Global Dayjs plugins initialised.")