Add root Dockerfile (standalone Next output, multi-stage pnpm build), drop
in-stack caddy in favor of publishing web's port for an external traefik
LXC (file-provider dynamic config included), and document the portainer
deploy flow.
Also fixes issues that blocked any production build: a bad auth-client
type cast, the ai SDK's mimeType->mediaType rename, an implicit-any
callback param, and push.ts eagerly calling webpush.setVapidDetails at
module import time (which crashed page-data collection whenever VAPID
env vars weren't present at build) — now lazily configured on first send.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>