feat(FN-833): add markdown render toggle for Agent Log viewer

- Add toggle button to switch between raw text and rendered markdown in AgentLogViewer
- Support markdown rendering with proper code syntax highlighting and line breaks
- Add CSS styles for rendered markdown content in agent log
- Add comprehensive tests for toggle behavior, markdown rendering, and edge cases
- Document the markdown render toggle feature in dashboard README

packages/dashboard/app/styles.css

@@ -3122,6 +3122,31 @@ body {
   overflow-wrap: break-word;
 }
 
+/* Agent Log markdown/plain-text mode toggle */
+.agent-log-mode-toggle {
+  padding: 3px 8px;
+  font-size: 11px;
+  font-weight: 500;
+  color: var(--text-muted);
+  background: var(--card);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-sm);
+  cursor: pointer;
+  transition: all 0.15s ease;
+  line-height: 1;
+}
+
+.agent-log-mode-toggle:hover {
+  background: var(--card-hover);
+  color: var(--text);
+}
+
+.agent-log-mode-toggle[aria-pressed="true"] {
+  background: var(--accent);
+  color: var(--text-on-accent, #fff);
+  border-color: var(--accent);
+}
+
 .detail-spec-edit-trigger {
   margin-bottom: var(--space-md);
 }