fix(web): mesh-stream wheel-scroll trap on landing page

The demo-dashboard embedded MeshStream with a fixed min-h-[480px] grid
+ overflow-y-auto on the message <ol>. Browsers capture every wheel
event that fires over a scrollable container — so hovering the demo
section froze page scroll until the user moved the cursor off.

Landing demo has only 6 messages, never needs internal scroll. The
fixed viewport only makes sense in the live dashboard where envelope
count can exceed the box.

Added `scrollable?: boolean` prop to MeshStream (default false).
- demo-dashboard (landing): no prop → intrinsic height, no overflow,
  wheel events propagate to the page
- live-stream-panel (/dashboard/meshes/[id]/live): scrollable → keeps
  the chat-style fixed viewport with scroll

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/modules/mesh/live-stream-panel.tsx

@@ -114,6 +114,7 @@ export const LiveStreamPanel = ({ meshId }: { meshId: string }) => {
         channelLabel="live-stream"
         emptyLabel={emptyLabel}
         footer={footer}
+        scrollable
       />
     </div>
   );