fix: preserve forwarded app origin on nginx redirects

[artiphishle]

Fixes #38.

Root cause

Generated Expo web exports can contain route directories such as products/index.html. The generated nginx config uses try_files $uri $uri/ /index.html, so a request for /products can resolve to the real /products/ directory and nginx emits its canonical trailing-slash redirect. Because nginx listens on the internal container port 8080, its default absolute redirect can leak that internal port through a kubectl port-forward whose browser-visible local port is different.

Fix

Apply absolute_redirect off; to the generated app nginx server. Nginx then emits relative redirects such as /products/, so the browser keeps the exact externally requested scheme/host/port while Expo Router's semantic /products route and static export layout remain unchanged.

The Minikube adapter applies this as a serving policy to the generated app image artifact and fails fast if the expected generated nginx Dockerfile is missing or its listen directive changes unexpectedly.

Coverage

Adds regression coverage that generated Minikube app images:

• disable absolute nginx redirects;
• keep the existing Expo static-route try_files behavior;
• do not use port_in_redirect off, which would still lose a non-default external forwarded port.

Includes a patch changeset.