🦞 改进：龙虾图标更生动

变更:
- 河里的龙虾主体改为 🦞
- 龙虾身上背着原来的小图标（如 🦸🔧 等）
- 小图标在右下角，白色圆形背景
- 龙虾主体更大（2.5em），带阴影效果

code/frontend/src/components/LobsterRiver/index.js

@@ -130,7 +130,8 @@ function LobsterRiver({ agents, onRefresh, onAgentToRiver, onAgentFromRiver }) {
               onMouseLeave={() => setHoveredAgent(null)}
               title={agent.name}
             >
-              <span className="agent-emoji">{agent.emoji}</span>
+              <span className="agent-emoji lobster-body">🦞</span>
+              <span className="agent-emoji agent-badge">{agent.emoji}</span>
               {hoveredAgent === agent.id && (
                 <span className="agent-name-tooltip">{agent.name}</span>
               )}
@@ -267,6 +268,23 @@ function LobsterRiver({ agents, onRefresh, onAgentToRiver, onAgentFromRiver }) {
         }
 
         .agent-emoji {
+        .lobster-body {
+          font-size: 2.5em;
+          filter: drop-shadow(0 2px 4px rgba(0, 0, 0, 0.3));
+        }
+
+        .agent-badge {
+          position: absolute;
+          bottom: -5px;
+          right: -5px;
+          font-size: 1.2em;
+          background: white;
+          border-radius: 50%;
+          padding: 2px;
+          box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
+        }
+          position: relative;
+          display: inline-block;
           filter: drop-shadow(0 2px 4px rgba(0, 0, 0, 0.3));
         }