chore: disable missing vite-plugin-checker

[3nprob]

https://github.com/headwaymaps/headway/actions/runs/19905547778/job/57060707239#step:4:2477

31  : ┆ [20.4s] | $ quasar build
31  : ┆ [20.6s] | 
31  : ┆ [20.6s] |  .d88888b.
31  : ┆ [20.6s] | d88P" "Y88b
31  : ┆ [20.6s] | 888     888
31  : ┆ [20.6s] | 888     888 888  888  8888b.  .d8888b   8888b.  888d888
31  : ┆ [20.6s] | 888     888 888  888     "88b 88K          "88b 888P"
31  : ┆ [20.6s] | 888 Y8b 888 888  888 .d888888 "Y8888b. .d888888 888
31  : ┆ [20.6s] | Y88b.Y8b88P Y88b 888 888  888      X88 888  888 888
31  : ┆ [20.6s] |  "Y888888"   "Y88888 "Y888888  88888P' "Y888888 888
31  : ┆ [20.6s] |        Y8b
31  : ┆ [20.6s] | 
31  : ┆ [20.8s] | 
31  : ┆ [20.8s] |  Build mode............. spa
31  : ┆ [20.8s] |  Pkg quasar............. v2.18.6
31  : ┆ [20.8s] |  Pkg @quasar/app-vite... v2.4.0
31  : ┆ [20.8s] |  Pkg vite............... v7.2.6
31  : ┆ [20.8s] |  Debugging.............. no
31  : ┆ [20.8s] |  Publishing............. no
31  : ┆ [20.8s] | 
31  : ┆ [21.0s] |  App • Using quasar.config.ts in "ts" format
31  : ┆ [21.0s] |  App • Running "@quasar/testing" Quasar App Extension...
31  : ┆ [21.1s] |  App • ⚠️  quasar.config file > invalid Vite plugin specified (cannot find it): vite-plugin-checker
31  : ┆ [21.1s] |  App •  WAIT  • Compiling of SPA UI with Vite in progress...

headway/services/frontend/www-app/quasar.config.ts

Line 88 in 67f6d7e

'vite-plugin-checker',

This removes the effectively unused checker.

Looks like re-enabling it involves addressing some type inconsistencies and/or further tweaking the plugin config: #400

[3nprob]

Closing in favor of #400.