feat: Add live streaming to Chat page

- Replace blocking execute_agent_task() with live subprocess streaming
- Use Popen() to read opencode output line-by-line in real-time
- Send 'chunk' events to frontend as agent thinks
- Frontend appends chunks incrementally for live response
- Matches Orchestrator's streaming UX
- No more waiting for complete response before seeing output

templates/chat.html

@@ -178,6 +178,11 @@ function sendChat(event) {
                 agentBadge.textContent = currentAgent;
               } else if (data.type === 'processing') {
                 chatStatus.innerHTML = `<span style="color:var(--info);">${data.message}</span>`;
+              } else if (data.type === 'chunk') {
+                // Live-Chunk empfangen - append to response
+                currentResponse += data.text;
+                responseText.textContent = currentResponse;
+                chatContainer.scrollTop = chatContainer.scrollHeight;
               } else if (data.type === 'response') {
                 currentResponse = data.text;
                 responseText.textContent = currentResponse;