Fix: OpenPPT vault‑tab preview images now load
The daemon served vault preview HTML with relative assets/… paths plus a <base href> pointing at the standalone vault file route, which 404s on the daemon origin — so the OpenPPT Design Vault tab template‑preview <img> broke inside the iframe.
rewriteVaultPreviewHtml now:
- strips the broken
<base>tag, and - rewrites both absolute
/api/designs/<slug>/(asset|file)/…and relativeassets/…references to the daemon's/api/vault/designs/<slug>/asset?path=…endpoint.
It runs on both the local and external‑proxy preview paths, so production (community / packaged) is covered. Regression test added (daemon suite 797 passing).