Restructure Web App into server/ + web/ (GsmNode parity)

Reorganize the Web App to match the GsmNode project layout: a Go
backend-for-frontend in server/ that embeds the built SPA and reverse-proxies
/api/* to the API Server, with the Vue 3 + Vite frontend moved into web/.

- Move all frontend files into web/ (history preserved via renames)
- Point vite build output at ../server/dist for Go embedding
- Add server/ Go BFF (main.go, go.mod, .env.example, Run-WebApp.ps1)
- Drop Docker/nginx deploy (Dockerfile, docker-compose.yml, nginx.conf.template,
  .dockerignore) in favor of the BFF, matching GsmNode
- Update .claude/launch.json to run the dev server from web/
- Rewrite README.md for the new layout

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Web App/server/.env.example

@@ -0,0 +1,8 @@
+# Web App (BFF) configuration
+
+# Address the Web App listens on
+WEB_ADDR=:8090
+
+# Base URL of the API Server. The BFF reverse-proxies /api/* to this host, so
+# the browser only ever talks same-origin to the Web App.
+API_BASE=http://localhost:8080