Add agent event viewer to task detail page

Update task detail page in Jr Web to show agent events:

1. Add 'Agent Log' section below task details 2. Connect to SSE endpoint when task is InProgress 3. Render events in a chat-like UI:

• Assistant messages: left-aligned, styled as chat bubbles
• Tool calls: collapsible, show tool name + args
• Tool results: nested under tool call, syntax-highlighted output
• Costs: subtle footer showing tokens/cost
• Errors: red alert style

4. For completed tasks, show historical events (GET /tasks/:id/events)

5. Auto-scroll to bottom as new events arrive

6. Add expand/collapse for long tool outputs (>20 lines)

CSS should be mobile-friendly and match existing Jr Web style.