fix(settings): shorten a commit sha in the colophon

pages.yml passes BUILD_VERSION: ${{ github.sha }}, so the colophon
shipped in 61e7093 was printing all forty characters of the sha. It now
shortens a long hex string to seven, the way git does.

Found in the deployed service worker, which embeds the same version
constant: o="61e7093c36f9a0111a5f1c8776aba4894c88ebc4".

The pattern requires at least one a-f, so a long run of digits that is
not a valid date can never be mistaken for a sha and truncated. Anything
that is not a timestamp or a sha is still printed exactly as the builder
gave it.

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

src/ui/buildVersion.ts

@@ -23,6 +23,13 @@ export function readBuildVersionEnv(): string | undefined {
 /** A millisecond epoch, which is what build.ts falls back to. */
 const EPOCH_MS = /^\d{10,}$/;
 
+/**
+ * A full commit sha. `pages.yml` passes `github.sha`, so the deployed colophon
+ * was printing all forty characters. Requires at least one a-f so a long run of
+ * digits that is not a valid date is never mistaken for one.
+ */
+const LONG_SHA = /^(?=.*[a-f])[0-9a-f]{12,}$/i;
+
 /**
  * `BUILD_VERSION` may be anything the person building chose — a git sha, a tag,
  * a release number — so an unrecognised value is printed as given rather than
@@ -39,6 +46,7 @@ export function describeBuild(raw: string | undefined): string {
     const at = new Date(Number(raw));
     if (!Number.isNaN(at.getTime())) return at.toISOString().slice(0, 10);
   }
+  if (LONG_SHA.test(raw)) return raw.slice(0, 7);
   return raw;
 }