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/.prettierrc.yml

@@ -0,0 +1,24 @@
+printWidth: 100
+tabWidth: 2
+useTabs: false
+semi: false
+singleQuote: false
+quoteProps: as-needed
+jsxSingleQuote: false
+trailingComma: es5
+bracketSpacing: true
+bracketSameLine: true
+arrowParens: always
+#rangeStart: 0
+#rangeEnd: n
+#parser:
+#filepath:
+#requirePragma: false
+#insertPragma: false
+#proseWrap: preserve
+htmlWhitespaceSensitivity: css
+#vueIndentScriptAndStyle: false
+endOfLine: lf
+#embeddedLanguageFormatting: auto
+# Enforce single attribute per line in HTML, Vue and JSX
+#singleAttributePerLine: false