fix(frontend): dynamic year + git commit hash in APP_VERSION

- Footer.svelte: replace hardcoded '2025' with new Date().getFullYear()
- build.sh: append git short hash to APP_VERSION for all bundle commands
  (bundle, bundle:embeddings, bundle:light). Format: '0.5.2+6f029903'.
  Previously only the tag was passed (e.g. '0.5.2'), and .git was not
  available in Docker context so vite.config.js fell back to '0.0.0'.

Verified: frontend assets contain '0.5.2+6f029903', getFullYear() replaces
hardcoded 2025.

frontend/src/lib/components/layout/Footer.svelte

@@ -9,6 +9,6 @@
 </script>
 
 <footer class="bg-surface-card border-t p-4 mt-8 text-center text-text-muted text-sm">
-  &copy; 2025 {$t.common.brand} <span class="font-mono">v{__APP_VERSION__}</span>
+  &copy; {new Date().getFullYear()} {$t.common.brand} <span class="font-mono">v{__APP_VERSION__}</span>
 </footer>
 <!-- #endregion Footer -->