homepage: live model info on the fleet cards, user docs page at /docs

- services.json: frank-large/medium/small move from admin-only to the user
  page with current descriptions (halogen w4b iGPU; 35:30 layer-split MTP
  27B on the R9700s; Gemma4-12B QAT vision path on the 3090) and docs
  links to /docs#models
- docs.html: static user documentation (access chain, model guide, media
  how-tos, troubleshooting); served at /docs via the post-auth homepage
  listener; shipped by deploy_homepage; footer + index link to it
- tests: pages seam asserts the docs contract (page, link, Caddy route,
  deployer copy)
- vault: Homepage.md synced (docs landing shipped, cards reclassified)

shared/homepage/index.html

@@ -16,6 +16,7 @@
 <main id="grid" class="grid"></main>
 <footer class="foot">
   <span>last master deployment: <span id="deployed-at"></span></span>
+  <a href="/docs">docs</a>
   <a href="/admin/">admin</a>
 </footer>
 <script src="deployed.js"></script>