feat(computes): the Computes page shows what each host has given its VMs

Each host is a row of what it has committed, read live from the host (in
parallel, by a 10 s deadline):

- Host: a status dot, the name, its address and details; when it cannot
  be reached, why.
- vCPUs: the overcommit ratio, large (warning above 2:1, red above
  4:1), over "N vCPUs on M CPUs" and the running VMs' share.
- Memory: memory given to all VMs against the host's memory, as one bar:
  running VMs dark, shut-off VMs light (they take their memory again
  when they start), and a line where the host's memory ends; red when
  the VMs were given more than the host has.
- Storage: the default pool (or the first) with its used share and free
  space; the others, a host may have dozens, open on a click.

A host that cannot be reached, or does not answer in time, says so in
one line instead. vCPUs and Memory sort by ratio and share. A host whose
read hangs is not read again until that read ends, so a stuck host keeps
at most one thread. The table's hidden status texts stay inside it, so
the page does not widen on a phone.

static/css/webvirtcloud.css

@@ -222,4 +222,65 @@ a {
     font-size: 12px;
     line-height: 1.5; /* If Placeholder of the input is moved up, rem/modify this. */
     border-radius: 2px;
-  }
+  }
+
+/* the Computes list: what each host has given its VMs */
+.compute-list td {
+    padding-top: 1rem;
+    padding-bottom: 1rem;
+}
+
+.compute-dot {
+    display: inline-block;
+    width: 0.6rem;
+    height: 0.6rem;
+    border-radius: 50%;
+    flex-shrink: 0;
+}
+
+.compute-ratio {
+    font-size: 1.5rem;
+    line-height: 1.2;
+    font-variant-numeric: tabular-nums;
+}
+
+.compute-memory {
+    min-width: 11rem;
+}
+
+.compute-storage {
+    min-width: 9rem;
+}
+
+/* a bar of given capacity: running VMs solid, shut-off VMs faint, and a
+   mark where the host's own capacity ends */
+.cap-bar {
+    position: relative;
+    display: flex;
+    height: 0.6rem;
+    border-radius: 0.3rem;
+    background: var(--bs-secondary-bg);
+}
+
+.cap-bar.cap-thin {
+    height: 0.3rem;
+}
+
+.cap-running {
+    background: var(--bs-primary);
+    border-radius: 0.3rem 0 0 0.3rem;
+}
+
+.cap-stopped {
+    background: var(--bs-primary);
+    opacity: 0.35;
+}
+
+.cap-host {
+    position: absolute;
+    top: -0.2rem;
+    bottom: -0.2rem;
+    width: 2px;
+    margin-left: -1px;
+    background: var(--bs-body-color);
+}