Fix vue assets under web base path (#711)

Remove hardcoded `--base=/app/` from npm build script and set `base:
'./'` in vite.config to generate relative asset URLs

Update server `updateBasePathInFrontend` to handle relative paths

Fixes #710

Signed-off-by: Rich C <richcarni@gmail.com>

frontend/vite.config.mjs

@@ -5,6 +5,7 @@ import vue from '@vitejs/plugin-vue'
 
 // https://vitejs.dev/config/
 export default defineConfig({
+  base: './',
   plugins: [vue()],
   resolve: {
     alias: {