dashboard: full-height square agent icon, icon-left card layout

The agent icon was a 26px <img> inline in the card head, hidden via
onerror when a stopped container's web server didn't answer — which
collapsed the slot and shifted the row.

Restructure the live container card as icon-left / body-right:
- the icon is a background-image div with aspect-ratio 1 and
  align-self stretch — full card height, square, and (being a
  background) it has no intrinsic size, so loading or failing it
  can never reflow the row;
- a failed load (stopped container) falls through to a placeholder
  fill instead of collapsing;
- the three content lines move into a .card-body column.

Tombstone rows keep the plain stacked layout (:not(.tombstone)).

closes #177

hive-c0re/assets/app.js

@@ -516,16 +516,22 @@
       const pending = transientsState.get(c.name)?.kind || null;
       const li = el('li', { class: 'container-row' + (pending ? ' pending' : '') });
 
-      // ── line 1: identity ─────────────────────────────────────────
+      // Full-height square agent icon, left of the card body. A
+      // background-image on a div (not <img>) contributes no intrinsic
+      // size, so loading or failing it can't shift the row layout, and
+      // a failed load (stopped container, web server down) just shows
+      // the placeholder fill — no broken-image glyph, no collapse.
+      // (issue #177)
+      const icon = el('div', {
+        class: 'container-icon',
+        style: `background-image:url("${url}icon")`,
+      });
+      // Card body: the three stacked content lines, right of the icon.
+      const body = el('div', { class: 'card-body' });
+
+      // ── identity ─────────────────────────────────────────────────
       const head = el('div', { class: 'head' });
       head.append(
-        // /icon always returns an image (the agent's configured SVG or
-        // the default hyperhive logo). onerror hides it for a stopped
-        // container whose web server isn't answering.
-        el('img', {
-          class: 'container-icon', src: url + 'icon', alt: '', loading: 'lazy',
-          onerror: "this.style.display='none'",
-        }),
         el('a', { class: 'name', href: url, target: '_blank', rel: 'noopener' }, c.name),
         el('span', { class: c.is_manager ? 'role role-m1nd' : 'role role-ag3nt' },
           c.is_manager ? 'm1nd' : 'ag3nt'),
@@ -582,9 +588,9 @@
           },
           `ctx·${k}k`));
       }
-      li.append(head);
+      body.append(head);
 
-      // ── line 2: action buttons ───────────────────────────────────
+      // ── action buttons ───────────────────────────────────────────
       const actions = el('div', { class: 'actions' });
       if (c.running) {
         actions.append(
@@ -623,9 +629,9 @@
             { purge: 'on' }, { noRefresh: true }),
         );
       }
-      li.append(actions);
+      body.append(actions);
 
-      // ── line 3: drill-ins ────────────────────────────────────────
+      // ── drill-ins ────────────────────────────────────────────────
       const drill = el('div', { class: 'drill-ins' });
       // Per-container journald viewer. Opens the side panel and
       // fetches the last N lines; refresh re-fetches; unit selector
@@ -641,8 +647,9 @@
           title: 'applied config repo on the hive forge',
         }, '↳ config repo ↗'));
       }
-      li.append(drill);
+      body.append(drill);
 
+      li.append(icon, body);
       ul.append(li);
     }
     root.append(ul);