Enable changelog subdomain routing on localhost

Open local changelogs at [slug].localhost:PORT — You can now visit changelogs in development using a subdomain like `http://my-project.localhost:4715`. The app rewrites those requests to the correct changelog page, matching production subdomain behavior. Modern browsers resolve `*.localhost` to `127.0.0.1` natively, so no /etc/hosts changes are required.

Enabled subdomain routing for changelogs in development so `http://[slug].localhost:PORT` maps to the corresponding changelog, matching production behavior.frontend
Updated the changelog URL builder to use the same subdomain pattern in both development and production (removed the previous path-based fallback).frontend
Clarified local behavior: modern browsers resolve `*.localhost` to `127.0.0.1`, so no `/etc/hosts` edits are necessary for local testing.devops

Updated local development environment notes to document the new localhost subdomain routing and the absence of required hosts file changes.devops