Guard formatCapacity against NaN/negative/used>total and a rounding edge case

Adversarial review of PR #20 flagged two narrow edge cases: malformed
remote-script output could produce NaN and render literally, and a
used>total race could show e.g. "510/500 GB". Also fixed a cosmetic
rounding bug where a value like 99.96 took the one-decimal branch and
toFixed(1) rounded it up to "100.0" instead of "100".

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/src/components/HostCard.tsx

@@ -18,7 +18,10 @@ function Bar({ label, pct }: { label: string; pct: number | null }) {
 // Picks a unit off total capacity, applies it to both sides so "used/total"
 // reads as e.g. "12.3/32 GB" instead of mixing MB and GB.
 function formatCapacity(used: number | null, total: number | null): string | null {
-  if (used === null || total === null || total <= 0) return null;
+  if (used === null || total === null || !Number.isFinite(used) || !Number.isFinite(total) || total <= 0) {
+    return null;
+  }
+  const clampedUsed = Math.min(Math.max(used, 0), total);
   const units: [number, string][] = [
     [1024 ** 4, "TB"],
     [1024 ** 3, "GB"],
@@ -26,8 +29,13 @@ function formatCapacity(used: number | null, total: number | null): string | nul
     [1024, "KB"],
   ];
   const [divisor, unit] = units.find(([d]) => total >= d) ?? [1, "B"];
-  const fmt = (n: number) => (n / divisor >= 100 ? (n / divisor).toFixed(0) : (n / divisor).toFixed(1));
+  // Decide decimal places off the *rounded* value -- otherwise e.g. 99.96
-  return `${fmt(used)}/${fmt(total)} ${unit}`;
+  // takes the one-decimal branch and toFixed(1) rounds it up to "100.0".
+  const fmt = (n: number) => {
+    const scaled = n / divisor;
+    return Math.round(scaled) >= 100 ? scaled.toFixed(0) : scaled.toFixed(1);
+  };
+  return `${fmt(clampedUsed)}/${fmt(total)} ${unit}`;
 }
 
 function formatUptime(sec: number | null): string {