fix(ui): replace hardcoded height calc with flex-1 to eliminate bottom blank area

All content panels used h-[calc(100vh-8rem)] which didn't match the
actual available space (CONTENT_TOP_OFFSET is 92px on Mac, 64px on
Win/Linux, not 128px), causing a visible gap at the bottom.

Replace with flex-1 min-h-0 to let panels fill the remaining space
after <main> and any sibling elements (e.g. OpenClaw health banner).

src/components/mcp/UnifiedMcpPanel.tsx

@@ -132,7 +132,7 @@ const UnifiedMcpPanel = React.forwardRef<
   };
 
   return (
-    <div className="px-6 flex flex-col h-[calc(100vh-8rem)] overflow-hidden">
+    <div className="px-6 flex flex-col flex-1 min-h-0 overflow-hidden">
       <AppCountBar
         totalLabel={t("mcp.serverCount", { count: serverEntries.length })}
         counts={enabledCounts}