Implement Server-Sent Events (SSE) for Real-time Agent Communication

- Add server-side SSE endpoint (/stream?from=N) for streaming state updates and messages
- Replace polling with SSE in frontend for real-time updates with significant performance improvements
- Implement efficient connection handling with backoff strategy for reconnections
- Add visual network status indicator in UI to show connection state
- Use non-blocking goroutine with channel pattern to handle SSE message delivery
- Ensure proper message sequencing and state synchronization between client and server
- Fix test suite to accommodate the new streaming architecture
- Update mocks to use conversation.Budget instead of ant.Budget

Co-Authored-By: sketch <hello@sketch.dev>
diff --git a/webui/src/web-components/sketch-app-shell.ts b/webui/src/web-components/sketch-app-shell.ts
index a540144..b73c83a 100644
--- a/webui/src/web-components/sketch-app-shell.ts
+++ b/webui/src/web-components/sketch-app-shell.ts
@@ -898,21 +898,6 @@
         const errorData = await response.text();
         throw new Error(`Server error: ${response.status} - ${errorData}`);
       }
-
-      // TOOD(philip): If the data manager is getting messages out of order, there's a bug?
-      // Reset data manager state to force a full refresh after sending a message
-      // This ensures we get all messages in the correct order
-      // Use private API for now - TODO: add a resetState() method to DataManager
-      (this.dataManager as any).nextFetchIndex = 0;
-      (this.dataManager as any).currentFetchStartIndex = 0;
-
-      // // If in diff view, switch to conversation view
-      // if (this.viewMode === "diff") {
-      //   await this.toggleViewMode("chat");
-      // }
-
-      // Refresh the timeline data to show the new message
-      await this.dataManager.fetchData();
     } catch (error) {
       console.error("Error sending chat message:", error);
       const statusText = document.getElementById("statusText");
@@ -1032,16 +1017,16 @@
             </div>
           </div>
 
-          <sketch-network-status
-            connection=${this.connectionStatus}
-            error=${this.connectionErrorMessage}
-          ></sketch-network-status>
-
           <sketch-call-status
             .agentState=${this.containerState?.agent_state}
             .llmCalls=${this.containerState?.outstanding_llm_calls || 0}
             .toolCalls=${this.containerState?.outstanding_tool_calls || []}
           ></sketch-call-status>
+
+          <sketch-network-status
+            connection=${this.connectionStatus}
+            error=${this.connectionErrorMessage}
+          ></sketch-network-status>
         </div>
       </div>
 
@@ -1127,9 +1112,6 @@
       }
     });
 
-    // Always enable polling by default
-    this.dataManager.setPollingEnabled(true);
-
     // Process any existing messages to find commit information
     if (this.messages && this.messages.length > 0) {
       this.updateLastCommitInfo(this.messages);