Add HDFS browser, SSH terminal, presentation editor, lab health panel

- HDFS WebHDFS file browser (api/hdfs_api.py + HdfsView)
- In-browser SSH terminal via paramiko WebSocket bridge (api/ssh_terminal.py + SshTerminal, xterm.js)
- Presentation deck editor (text + image upload) and CRUD endpoints
- Collapsible GPU matrix + new LabHealthPanel in SideNav
- Topology fixes (edge alignment, Hadoop node, compact nodes)
- nginx ws timeout bump for long-lived SSH sessions

api/presentation.py

@@ -245,6 +245,7 @@ header .meta{{font-size:.75rem;opacity:.7}}
 .slide ul{{list-style:none;font-size:1.15rem;line-height:1.9}}
 .slide li::before{{content:"▸ ";color:#60a5fa}}
 .slide.hero h2{{font-size:3.2rem}}
+.slide img.slide-img{{max-height:42vh;max-width:100%;margin-top:1.5rem;border-radius:10px;border:1px solid rgba(96,165,250,.25);box-shadow:0 8px 30px rgba(0,0,0,.4);object-fit:contain}}
 nav{{display:flex;gap:.5rem;padding:1rem 2rem;border-top:1px solid rgba(96,165,250,.2);align-items:center}}
 nav button{{background:#1e3a5f;border:1px solid rgba(96,165,250,.3);color:#e8f1ff;padding:.5rem 1rem;border-radius:6px;cursor:pointer}}
 nav button:hover{{background:#234876}}
@@ -275,7 +276,8 @@ slides.forEach((s,idx)=>{{
   const el=document.createElement("section");
   el.className="slide"+(s.kind==="hero"?" hero":"")+(idx===0?" active":"");
   const bullets=(s.bullets||[]).map(b=>"<li>"+b+"</li>").join("");
-  el.innerHTML="<h2>"+s.title+"</h2><h3>"+(s.subtitle||"")+"</h3><ul>"+bullets+"</ul>";
+  const img=s.image?'<img class="slide-img" src="'+s.image+'" alt=""/>':"";
+  el.innerHTML="<h2>"+s.title+"</h2><h3>"+(s.subtitle||"")+"</h3><ul>"+bullets+"</ul>"+img;
   container.appendChild(el);
   const d=document.createElement("button");
   d.className="dot"+(idx===0?" active":"");