ci: build gitea-local-fork and push to attic

Add the renamed gitea-local-fork derivation to the Woodpecker
build matrix on x86_64 and aarch64 (the only platforms the
derivation supports — see flake.nix). Resulting closure is
pushed to attic-infra-cache-k3s-1 so subsequent
`just gitea-run` invocations resolve from cache rather than
recompile Go 1.26.3 locally.

ci/build.py

@@ -61,6 +61,11 @@ packages = ["hello-world", "geesefs", "xonsh"]
 #     packages += ["google-antigravity", "google-antigravity-no-fhs"]
 if ARCH == "s390x-linux":
     packages += ["attic-client"]
+# gitea-local-fork: only defined for x86_64-linux and aarch64-linux (cgo+sqlite
+# and pnpm don't cross-compile cleanly — see flake.nix). Slow build: Go 1.26.3
+# compiles from source (~5-8 min cold) on the first push after a rev bump.
+if ARCH in ("x86_64-linux", "aarch64-linux"):
+    packages += ["gitea-local-fork"]
 
 print("Building packages...")
 for pkg in packages: