feat: wire up application logs from OpenSearch, fix event autoscroll

Add GET /api/v1/logs endpoint to query application logs stored in
OpenSearch with filters for application, agent, level, time range,
and text search. Wire up the AgentInstance LogViewer with real data
and an EventFeed-style toolbar (search input + level filter pills).

Fix agent events timeline autoscroll by reversing the DESC-ordered
events so newest entries appear at the bottom where EventFeed
autoscrolls to.

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

ui/src/pages/AgentHealth/AgentHealth.tsx

@@ -256,7 +256,7 @@ export default function AgentHealth() {
                 : ('running' as const),
         message: `${e.agentId}: ${e.eventType}${e.detail ? ' \u2014 ' + e.detail : ''}`,
         timestamp: new Date(e.timestamp),
-      })),
+      })).toReversed(),
     [events],
   );