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/agents/AgentsPanel.tsx

@@ -6,7 +6,7 @@ interface AgentsPanelProps {
 
 export function AgentsPanel({}: AgentsPanelProps) {
   return (
-    <div className="px-6 flex flex-col h-[calc(100vh-8rem)]">
+    <div className="px-6 flex flex-col flex-1 min-h-0">
       <div className="flex-1 glass-card rounded-xl p-8 flex flex-col items-center justify-center text-center space-y-4">
         <div className="w-20 h-20 rounded-full bg-white/5 flex items-center justify-center mb-4 animate-pulse-slow">
           <Bot className="w-10 h-10 text-muted-foreground" />