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/utils/department-utils/index.ts

@@ -0,0 +1,28 @@
+import { type TreeDataNode } from "antd"
+import type { TreeNode } from "@/types/tree"
+import type { Department } from "@/types/entity"
+
+export function transformDepartmentData(departments: TreeNode<Department>[]): TreeDataNode[] {
+  if (!departments || departments.length === 0) {
+    return []
+  }
+
+  return departments
+    .sort((a, b) => a.item.sort - b.item.sort)
+    .map((node) => {
+      const { item, children } = node
+      const hasChildren = children && children.length > 0
+
+      const treeItem: TreeDataNode = {
+        key: item.id,
+        title: item.name,
+      }
+
+      if (hasChildren) {
+        // Append children
+        return { ...treeItem, children: transformDepartmentData(children) }
+      }
+
+      return treeItem
+    })
+}