Stable .localhost URLs in development (portless adoption)

This one is for the contributor side of the project, not the user side — but worth noting.

epotli's development setup now uses portless for local URLs. The dev server runs at https://kids-games.localhost (or https://<branch>.kids-games.localhost for parallel branches), instead of the random ports that Next.js dev usually picks.

What changes for contributors:

• Bookmarks survive between dev sessions.
• HTTPS works out of the box (useful for testing service workers, PWAs, and clipboard APIs).
• Multiple branches can run side by side without port conflicts.

What does not change for users:

• The live site at epotli.com is unaffected.
• No production behaviour shifts.

Anyone running the project locally needs a one-time portless hosts sync after pulling. Everything else is the same pnpm dev workflow.

Read the project README if you are setting up a fresh dev environment.