Fix system message height estimation to use user sizing rules

The condition was changed from 'message.role === "assistant"' to
'message.role !== "user"', which inadvertently routed system messages
into assistant sizing (72 chars/line, 78px base, no attachments) instead
of user sizing (56 chars/line, 96px base, attachment-aware). Restore the
original branching logic so system messages fall through to user sizing.

Co-authored-by: Julius Marminge <juliusmarminge@users.noreply.github.com>

Author: cursoragent

apps/web/src/components/timelineHeight.ts

@@ -67,7 +67,7 @@ export function estimateTimelineMessageHeight(
   message: TimelineMessageHeightInput,
   layout: TimelineHeightEstimateLayout = { timelineWidthPx: null },
 ): number {
-  if (message.role !== "user") {
+  if (message.role === "assistant") {
     const charsPerLine = estimateCharsPerLineForAssistant(layout.timelineWidthPx);
     const estimatedLines = estimateWrappedLineCount(message.text, charsPerLine);
     return ASSISTANT_BASE_HEIGHT_PX + estimatedLines * LINE_HEIGHT_PX;