docs(readme): the module system shipped

The quick start carried a caveat telling a visitor that the Modules screen it
had just described was not on `main` yet, and that a checkout served the Ultima
Online features from core directly. The cutover merged on 2026-08-12
(website#150), so both halves of that are now false and the caveat contradicts
the page around it.

Replaced rather than deleted: a reader who saw the old note deserves to know it
resolved, and the sentence that replaces it is the one fact the front page owes
about the change - a `main` checkout is a game-agnostic core, and Ultima Online
arrives as the module the section above tells you to install.

Nothing else on the page needed touching. It was written describing the module
system as the shape of the project rather than as work in progress, which is
what left exactly one paragraph to retire.

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -141,10 +141,9 @@ A compose-managed host can declare the set instead of clicking, with
 `MODULES=uo@0.3.0=<that URL>` — resolution at container start is idempotent and offline-safe,
 so a restart with the network down brings the site up exactly as it was.
 
-> The module system is landing: it lives on the website's **`edge`** branch and reaches `main`
+> **The module system shipped on 2026-08-12** and this is now simply how the site works — a
-> as one cutover at the end of the current workstream. A `main` checkout today serves the
+> `main` checkout is a game-agnostic core with a Modules screen, and Ultima Online arrives as
-> Ultima Online features from core directly and has no Modules screen — same site, same URLs,
+> the module above or not at all.
-> nothing to install.
 
 **A game that is not Ultima Online?** That is what the
 [**Integration-kit**](https://gitea.whitlocktech.com/RunicGateway/Integration-kit) is for —