fix(demo): never leak the release-server IP in the public demo

- Companion QR overlay: demo builds encode the demo's own origin
  (/packages/archipelago-companion.apk ships in the web image) instead of
  the vps2 raw URL.
- Dockerfile.web/.backend: build-time scrub replaces every remaining
  occurrence of the release-server address with registry.demo.internal and
  fails the build if any survives.
- Mock backend update-mirror list, sideload help text, and changelog prose
  no longer name the server address.
- Copy demo-images workflow into .gitea/workflows/ — Gitea ignores
  .github/workflows when .gitea/workflows exists, so the CI never ran.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

neode-ui/Dockerfile.web

@@ -29,6 +29,20 @@ ENV VITE_DEMO=$VITE_DEMO
 # Use npm script which handles build better
 RUN npm run build:docker || (echo "Build failed! Listing files:" && ls -la && echo "Checking vite config:" && cat vite.config.ts && exit 1)
 
+# Demo builds must not leak the private release/registry server address anywhere
+# in the served bundle (JS constants, catalog.json, prose). Replace every
+# occurrence with a non-routable placeholder, then fail the build if any slipped
+# through. (The companion-QR URL is handled in source — it needs a URL that works.)
+RUN if [ "$VITE_DEMO" = "1" ] || [ "$VITE_DEMO" = "true" ]; then \
+      find dist -type f \( -name '*.js' -o -name '*.mjs' -o -name '*.css' -o -name '*.html' \
+        -o -name '*.json' -o -name '*.map' -o -name '*.txt' -o -name '*.webmanifest' \) \
+        -exec sed -i \
+          -e 's#146\.59\.87\.168:3000/lfg2025#registry.demo.internal/archy#g' \
+          -e 's#146\.59\.87\.168:3000#registry.demo.internal#g' \
+          -e 's#146\.59\.87\.168#registry.demo.internal#g' {} + && \
+      if grep -rq '146\.59\.87\.168' dist; then echo 'LEAK: release-server IP still in dist'; exit 1; fi; \
+    fi
+
 # Production stage
 FROM nginx:alpine