fix: increase message body truncation from 300 to 800 chars in Web UI

DM messages from agents were cut off at 300 characters in the
MessageList view. Increased to 800 to show more context while
still keeping long messages manageable.

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

web/src/lib/components/MessageList.svelte

@@ -116,7 +116,7 @@
 								<span class="badge bg-accent-yellow/20 text-accent-yellow">P{msg.priority}</span>
 							{/if}
 						</div>
-						<div class="text-sm text-text-primary/90 leading-relaxed"><MessageBody body={msg.body} truncate={300} /></div>
+						<div class="text-sm text-text-primary/90 leading-relaxed"><MessageBody body={msg.body} truncate={800} /></div>
 
 						<!-- Attachments -->
 						{#if msg.attachments && msg.attachments.length > 0}