Stop the rc unit failing before the first RC is cut

The rc service fetched and reset /root/omarchy-pkgs-rc in ExecStartPre, but
that worktree does not exist until the first RC creates the rc branch — so on
a freshly set up host the unit failed every five minutes, forever, and showed
up as a failed unit in the timer report.

It now runs bin/auto-release-rc from the main checkout, which always exists:
nothing queued exits silently, no rc branch is a clean no-op, and a missing
worktree is created on demand before handing off to the worktree's own
auto-release.

systemd/omarchy-auto-release-rc.service

@@ -5,13 +5,11 @@ Wants=network-online.target
 
 [Service]
 Type=oneshot
-# The rc channel builds from the rc branch worktree, but publishes into the
-# primary checkout's channel tree via OMARCHY_REPO_ROOT. The rc branch is
-# rebuilt (master + pin commits) each release train and force-pushed, so this
-# worktree follows with a hard reset rather than a fast-forward pull.
-ExecStartPre=/usr/bin/git -C /root/omarchy-pkgs-rc fetch origin rc
-ExecStartPre=/usr/bin/git -C /root/omarchy-pkgs-rc reset --hard origin/rc
-ExecStart=/bin/bash -c 'source /root/.omarchy/build-credentials && /root/omarchy-pkgs-rc/bin/auto-release rc'
+# Runs from the main checkout: bin/auto-release-rc creates and syncs the rc
+# branch worktree itself, so a host with no rc branch yet is a no-op instead
+# of a unit that fails every five minutes. Builds happen in the worktree but
+# publish into the primary checkout's channel tree via OMARCHY_REPO_ROOT.
+ExecStart=/bin/bash -c 'source /root/.omarchy/build-credentials && /root/omarchy-pkgs/bin/auto-release-rc'
 Environment=OMARCHY_STATE_DIR=/root/.state
 Environment=OMARCHY_REPO_ROOT=/root/omarchy-pkgs/pkgs.omarchy.org
 TimeoutStartSec=7200