feat(web): implement SSE chat streaming with real-time token rendering (#516)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/web/src/components/chat/Chat.test.tsx

@@ -64,10 +64,12 @@ function createMockUseChatReturn(
       },
     ],
     isLoading: false,
+    isStreaming: false,
     error: null,
     conversationId: null,
     conversationTitle: null,
     sendMessage: vi.fn().mockResolvedValue(undefined),
+    abortStream: vi.fn(),
     loadConversation: vi.fn().mockResolvedValue(undefined),
     startNewConversation: vi.fn(),
     setMessages: vi.fn(),