fix(dashboard): robust tool call display and filter logic

Two fixes for tool call display in the dashboard:

1. **filterDisplayMessages includes tool_calls** (MessageBubble.js)
   Previously filtered out messages with only tool_calls (no content/thinking).
   Now correctly keeps messages that have tool_calls.

2. **Type-safe getToolSummary** (markdown.js)
   The heuristic tool summary extractor was calling .slice() without
   type checks. If a tool input had a non-string value (e.g., number),
   it would throw TypeError. Now uses a helper function to safely
   check types before calling string methods.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

dashboard/components/MessageBubble.js

@@ -44,11 +44,11 @@ export function MessageBubble({ msg, userBg, compact = false, formatTime }) {
 }
 
 /**
- * Filter messages for display — removes tool-call-only messages
- * that have no text or thinking (would render as empty bubbles).
+ * Filter messages for display — removes empty assistant messages
+ * (no content, thinking, or tool_calls) that would render as empty bubbles.
  */
 export function filterDisplayMessages(messages) {
   return messages.filter(msg =>
-    msg.content || msg.thinking || msg.role === 'user'
+    msg.content || msg.thinking || msg.tool_calls?.length || msg.role === 'user'
   );
 }