Name the server OMARCHY_REPO_HOST, not OMARCHY_BUILD_HOST

Builds now happen wherever the operator likes, so naming the destination after
building described the old arrangement rather than the current one. What the
push and deploy commands reach is the machine that serves pkgs.omarchy.org and
holds the signing key: the repository host. It also runs the scheduled builds,
which is why the trigger in omarchy-pkgs release points at the same place.

Resolution moves into helpers/host-helpers.sh, which all three commands now
share instead of repeating: --host, then OMARCHY_REPO_HOST, then .repo-host.
OMARCHY_BUILD_HOST and .build-host keep working as fallbacks, so existing
environments and checkouts are unaffected.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitignore

@@ -34,3 +34,4 @@ pkgbuilds/symfony-cli/symfony*
 pkgbuilds/yay/yay/
 .srcdest/
 .build-host
+.repo-host