feat: add Logs tab with cursor-paginated search, level filters, and live tail

- Extend GET /api/v1/logs with cursor pagination, multi-level filtering,
  optional application scoping, and level count aggregation
- Add exchangeId, instanceId, application, mdc fields to log responses
- Refactor ClickHouseLogStore with keyset pagination (N+1 pattern)
- Add LogSearchRequest/LogSearchResponse core domain records
- Create LogSearchPageResponse wrapper DTO
- Add Logs as 4th content tab (Exchanges | Dashboard | Runtime | Logs)
- Implement LogSearch component with debounced search, level filter bar,
  expandable log entries, cursor pagination, and live tail mode
- Add cross-navigation: exchange header → logs, log tab → logs tab
- Update ClickHouseLogStoreIT with cursor, multi-level, cross-app tests

Closes: #104

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

ui/src/components/ContentTabs.tsx

@@ -7,6 +7,7 @@ const TABS = [
   { label: 'Exchanges', value: 'exchanges' },
   { label: 'Dashboard', value: 'dashboard' },
   { label: 'Runtime', value: 'runtime' },
+  { label: 'Logs', value: 'logs' },
 ];
 
 interface ContentTabsProps {

ui/src/components/ExecutionDiagram/tabs/LogTab.tsx

@@ -1,4 +1,5 @@
 import { useState, useMemo } from 'react';
+import { useNavigate } from 'react-router';
 import { useApplicationLogs } from '../../../api/queries/logs';
 import type { LogEntryResponse } from '../../../api/queries/logs';
 import styles from '../ExecutionDiagram.module.css';
@@ -30,6 +31,7 @@ function formatTime(iso: string): string {
 
 export function LogTab({ applicationId, exchangeId, processorId }: LogTabProps) {
   const [filter, setFilter] = useState('');
+  const navigate = useNavigate();
 
   const { data: logs, isLoading } = useApplicationLogs(
     applicationId,
@@ -93,23 +95,35 @@ export function LogTab({ applicationId, exchangeId, processorId }: LogTabProps)
             {processorId ? 'No logs for this processor' : 'No logs available'}
           </div>
         ) : (
-          <table style={{ width: '100%', borderCollapse: 'collapse' }}>
-            <tbody>
-              {entries.map((entry, i) => (
-                <tr key={i} style={{ borderBottom: '1px solid var(--border-subtle)' }}>
-                  <td style={{ padding: '3px 6px', whiteSpace: 'nowrap', color: 'var(--text-muted)' }}>
-                    {formatTime(entry.timestamp)}
-                  </td>
-                  <td style={{ padding: '3px 4px', whiteSpace: 'nowrap', fontWeight: 600, color: levelColor(entry.level), width: '40px' }}>
-                    {entry.level}
-                  </td>
-                  <td style={{ padding: '3px 6px', color: 'var(--text-primary)', wordBreak: 'break-word' }}>
-                    {entry.message}
-                  </td>
-                </tr>
-              ))}
-            </tbody>
-          </table>
+          <>
+            <table style={{ width: '100%', borderCollapse: 'collapse' }}>
+              <tbody>
+                {entries.map((entry, i) => (
+                  <tr key={i} style={{ borderBottom: '1px solid var(--border-subtle)' }}>
+                    <td style={{ padding: '3px 6px', whiteSpace: 'nowrap', color: 'var(--text-muted)' }}>
+                      {formatTime(entry.timestamp)}
+                    </td>
+                    <td style={{ padding: '3px 4px', whiteSpace: 'nowrap', fontWeight: 600, color: levelColor(entry.level), width: '40px' }}>
+                      {entry.level}
+                    </td>
+                    <td style={{ padding: '3px 6px', color: 'var(--text-primary)', wordBreak: 'break-word' }}>
+                      {entry.message}
+                    </td>
+                  </tr>
+                ))}
+              </tbody>
+            </table>
+            {exchangeId && (
+              <div style={{ padding: '6px 10px', borderTop: '1px solid var(--border-subtle)', fontSize: '11px', textAlign: 'center' }}>
+                <button
+                  onClick={() => navigate(`/logs/${applicationId}?exchangeId=${exchangeId}`)}
+                  style={{ background: 'none', border: 'none', color: 'var(--amber)', cursor: 'pointer', fontSize: '11px', fontFamily: 'var(--font-body)' }}
+                >
+                  Open in Logs tab {'\u2192'}
+                </button>
+              </div>
+            )}
+          </>
         )}
       </div>
     </div>