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/phone-number-utils/index.ts

@@ -0,0 +1,28 @@
+import { type CountryCode as RegionAbbreviation, getCountryCallingCode, parsePhoneNumberWithError, PhoneNumber } from "libphonenumber-js"
+
+/**
+ * Format user's phone number as user's country/region.
+ *
+ * @param regionAbbreviation user's region abbreviation
+ * @param phoneNumber user's phone number
+ * @return formatted phone number
+ */
+export function formatInternationalPhoneNumber(regionAbbreviation: string, phoneNumber: string): string {
+  try {
+    const _phoneNumber = parsePhoneNumberWithError(phoneNumber, regionAbbreviation as RegionAbbreviation)
+
+    if (!_phoneNumber.isValid()) {
+      console.warn(`Phone number ${_phoneNumber.formatInternational()} is not valid`)
+    }
+    return _phoneNumber.formatInternational()
+  } catch (error) {
+    console.error("Phone number parsing failed:", error)
+    const _regionAbbreviation: RegionAbbreviation = regionAbbreviation as RegionAbbreviation
+    const callingCode = getCountryCallingCode(_regionAbbreviation)
+    return `+${callingCode} ${phoneNumber}`
+  }
+}
+
+export function getDefaultCountryCode(): RegionAbbreviation {
+  return import.meta.env.VITE_DEFAULT_REGION_CODE
+}