fix(site): --out printed a repo-relative path for a directory outside the repo

`relative(REPO, OUT)` is true and useless once the target is elsewhere: rendering into
a temp directory reported `../../tmp/mo-ref-out-XXXX/site-reference/ is fresh`. The
label now falls back to the absolute path whenever the relative one escapes the repo,
and the default path still reads `site-reference/`.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NynrRND6ZUwGvq3ZUTCfxG

Author: dmealing

scripts/build-site-reference.ts

@@ -62,8 +62,13 @@ function resolveOut(): string {
   return out;
 }
 const OUT = resolveOut();
-/** How the messages below name the target — `site-reference/` on the default path. */
-const label = `${relative(REPO, OUT) || OUT}/`;
+/**
+ * How the messages below name the target — `site-reference/` on the default path, and an
+ * absolute path for anything outside the repo (a repo-relative `../../tmp/x` would be
+ * true and useless).
+ */
+const rel = relative(REPO, OUT);
+const label = rel !== "" && !rel.startsWith("..") ? `${rel}/` : OUT;
 
 /** Every file under `dir`, repo-relative, sorted. */
 function walk(dir: string, root: string = dir): string[] {