fix(ui): make Vite HMR reliable on shared filesystems

[SirEdvin]

Summary

• Enables Vite polling-based file watching so HMR catches source edits on WSL/VM/shared/bind-mounted filesystems.
• Keeps the existing /api proxy and WebSocket proxy behavior unchanged.

Verification

• npm run test — 25 files / 180 tests passed
• npm run build — passed
• Playwright HMR smoke: changed a visible landing-page string and observed the browser update without page.reload(), then restored the file
• Docker smoke:
  • backend image /health returned {"status":"ok"}
  • frontend nginx image served index.html containing <div id="root"></div>

PR test images

• registry.siredvin.home/archflow-backend:0.1.0-vite-hmr-polling-c2155e4
  • digest: sha256:68f535ce035a2039394c51a110f2119cc9a32ba409c03f30dac182719f2d126b
• registry.siredvin.home/archflow-frontend:0.1.0-vite-hmr-polling-c2155e4
  • digest: sha256:a393f44b4644fb3edbcf7c49983f7ead8a17712fa26aeb1fcfe37ec811cbdaef
• Scoped aliases also pushed:
  • registry.siredvin.home/archflow-backend:vite-hmr-polling-latest
  • registry.siredvin.home/archflow-frontend:vite-hmr-polling-latest

Note: this publishes test images only; no HomelabInfrastructure deployment change is included.