docs: record that CI, the registry and the deploy moved to Gitea

The pipeline change made a set of sentences false, and they are the only
record of why things are the way they are, so they move with it: the CI
section and deploy target in README, the cron and BASE_PATH notes in
ARCHITECTURE, the documented User-Agent in INGESTION, and the contact
URL in SOURCES.

Two comments in source were false in the same way and are fixed here
rather than left for the next reader. `serve.ts` said compression was
"the whole difference between the Docker image and the deployed site" —
the image *is* the deployed site now, so that negotiation is the only
compression any reader gets. `robots.ts` justified product-token
matching with "our contact URL contains the string StereotypicalCat",
which it no longer does; the hazard is the arbitrary substring, not that
one, so the comment now says so and the regression test keeps the URL
that actually caused it.

What is deliberately NOT rewritten: game8.co's refusal stays in the past
tense with the Gitea result marked unverified, in AGENTS.md, README,
SOURCES and FEEDBACK alike. A new runner address is the variable that
failure turns on, so it may well be served — but "may well be" is not
evidence, and the four places that would have to change are named
together so they change together once a cycle has actually run.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

serve.ts

@@ -23,10 +23,12 @@ const ROOT_DIR = resolve(ROOT);
  * times the bytes and, on anything slower than a laptop on wifi, three times the
  * download.
  *
- * GitHub Pages compresses for us, so the deployed site never had this problem;
- * the Docker image serves through this file and did. An image whose payload is
- * 3x the site's is not a placeholder detail — it is the only thing a self-hoster
- * ever sees.
+ * This used to be the self-hoster's problem only: GitHub Pages compressed for
+ * us, so the deployed site never had it, while the Docker image serves through
+ * this file and did. Since the move to Gitea the image *is* the deploy, so this
+ * is now the only compression the deployed site gets — there is no host behind
+ * it doing the job silently. Serving 3x the bytes is not a placeholder detail
+ * when it is what every reader gets.
  */
 const COMPRESSIBLE = new Set([
   ".html",