feat: add agent dropdown for task assignment

- Replace assignee text input with select dropdown
- Populate dropdown with agents from /api/agents endpoint
- Add styling to match existing form elements
- Improves UX by preventing typos and showing available agents

public/app.js

@@ -270,3 +270,32 @@ ws.onmessage = (event) => {
     loadTasks();
   }
 };
+
+// Populate agent dropdown
+async function populateAgentDropdown() {
+  try {
+    const res = await fetch('/api/agents');
+    const agents = await res.json();
+    
+    const select = document.getElementById('assignee');
+    if (!select) return;
+    
+    // Clear existing options except the first placeholder
+    select.innerHTML = '<option value="">Select agent...</option>';
+    
+    // Add agent options
+    agents.forEach(agent => {
+      const option = document.createElement('option');
+      option.value = agent.name;
+      option.textContent = agent.name;
+      select.appendChild(option);
+    });
+  } catch (err) {
+    console.error('Failed to load agents for dropdown:', err);
+  }
+}
+
+// Populate dropdown on page load
+document.addEventListener('DOMContentLoaded', () => {
+  populateAgentDropdown();
+});