feat(deploy): dockerize web app for portainer git-stack deploy behind external traefik

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>

apps/web/app/(auth)/login/page.tsx

@@ -135,7 +135,7 @@ function SocialButton({ provider, label, icon }: { provider: "github" | "discord
 function AuthentikButton({ label }: { label: string }) {
   if (!process.env["NEXT_PUBLIC_AUTHENTIK_ENABLED"]) return null;
   return (
-    <Button variant="outline" className="w-full gap-2" type="button" onClick={() => (authClient as { signIn: { genericOAuth: (opts: { providerId: string; callbackURL: string }) => Promise<void> } }).signIn.genericOAuth({ providerId: "authentik", callbackURL: "/recipes" })}>
+    <Button variant="outline" className="w-full gap-2" type="button" onClick={() => (authClient as unknown as { signIn: { genericOAuth: (opts: { providerId: string; callbackURL: string }) => Promise<void> } }).signIn.genericOAuth({ providerId: "authentik", callbackURL: "/recipes" })}>
       <AuthentikIcon />
       {label}
     </Button>