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/vite.config.ts

@@ -0,0 +1,18 @@
+import { fileURLToPath, URL } from "node:url"
+import { defineConfig } from "vite"
+import react from "@vitejs/plugin-react"
+import tailwindcss from "@tailwindcss/vite"
+import svgr from "vite-plugin-svgr"
+
+// https://vite.dev/config/
+export default defineConfig({
+  plugins: [react(), tailwindcss(), svgr()],
+  resolve: {
+    alias: {
+      "@": fileURLToPath(new URL("./src", import.meta.url)),
+    },
+  },
+  server: {
+    allowedHosts: true,
+  }
+})