v0.8.0 — Update-available detection (version chip + changelog)

Footer becomes a changelog chip and shows an 'Update available' badge when a
newer APP_VERSION exists upstream. Detection reads src/lib/version.ts from the
Gitea default branch (dms model) and compares — self-contained, no OTM control
plane. Adds src/lib/update-check.ts and GET /api/version (also a running-version
probe for the upcoming one-click rebuild).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app/api/version/route.ts

@@ -0,0 +1,19 @@
+import { NextResponse } from "next/server";
+import { requireAuth } from "@/lib/auth";
+import { getUpdateStatus } from "@/lib/update-check";
+
+export const dynamic = "force-dynamic";
+
+// Running-version probe + upstream update check. Used by the footer chip, and
+// (later) polled by the self-update UI to detect when the rebuilt instance is
+// back online on the new version.
+export async function GET() {
+  try {
+    await requireAuth();
+  } catch {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+  return NextResponse.json(await getUpdateStatus(), {
+    headers: { "Cache-Control": "no-store" },
+  });
+}