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

- Implement streamChatMessage() using fetch ReadableStream for SSE parsing
- Update useChat hook with streaming state, abort support, and fallback to non-streaming
- Add streaming indicator (blinking cursor) in MessageList during token streaming
- Update ChatInput with Stop button during streaming, disable input while streaming
- Add CSS animations for streaming cursor
- Fix message ID uniqueness to prevent collisions in rapid sends
- Update tests for streaming path with makeStreamSucceed/makeStreamFail helpers

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/app/globals.css

@@ -765,6 +765,28 @@ body::before {
   animation: scaleIn 0.1s ease-out;
 }
 
+/* Streaming cursor for real-time token rendering */
+@keyframes streaming-cursor-blink {
+  0%,
+  100% {
+    opacity: 1;
+  }
+  50% {
+    opacity: 0;
+  }
+}
+
+.streaming-cursor {
+  display: inline-block;
+  width: 2px;
+  height: 1em;
+  background-color: rgb(var(--accent-primary));
+  border-radius: 1px;
+  animation: streaming-cursor-blink 1s step-end infinite;
+  vertical-align: text-bottom;
+  margin-left: 1px;
+}
+
 /* -----------------------------------------------------------------------------
    Dashboard Layout — Responsive Grids
    ----------------------------------------------------------------------------- */