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/eslint.config.js

@@ -0,0 +1,42 @@
+import js from "@eslint/js"
+import globals from "globals"
+import reactHooks from "eslint-plugin-react-hooks"
+import reactRefresh from "eslint-plugin-react-refresh"
+import tseslint from "typescript-eslint"
+import { globalIgnores } from "eslint/config"
+
+export default tseslint.config([
+  globalIgnores(["dist"]),
+  {
+    files: ["**/*.{ts,tsx}"],
+    extends: [
+      js.configs.recommended,
+      reactHooks.configs["recommended-latest"],
+      reactRefresh.configs.vite,
+      // Remove tseslint.configs.recommended and use this for stricter rules
+      ...tseslint.configs.strictTypeChecked,
+    ],
+    languageOptions: {
+      ecmaVersion: 2020,
+      globals: globals.browser,
+      parserOptions: {
+        project: ["./tsconfig.node.json", "./tsconfig.app.json"],
+        tsconfigRootDir: import.meta.dirname,
+      },
+    },
+    rules: {
+      "@typescript-eslint/no-unused-vars": 0,
+      "@typescript-eslint/no-non-null-assertion": 0,
+      "@typescript-eslint/restrict-template-expressions": 0,
+      "@typescript-eslint/no-unsafe-assignment": 0,
+      "@typescript-eslint/no-unsafe-call": 0,
+      "no-empty": 0,
+      "@typescript-eslint/no-unsafe-member-access": 0,
+      "no-empty-pattern": 0,
+      "@typescript-eslint/no-unnecessary-condition": 0,
+      "@typescript-eslint/no-confusing-void-expression": 0,
+      "@typescript-eslint/no-empty-object-type": 0,
+      "react-refresh/only-export-components": 0,
+    },
+  },
+])