fix: improve duration formatting (Xm Ys) and truncate exchange IDs

- formatDuration and formatDurationShort now show Xm Ys for durations >= 60s (e.g. "5m 21s" instead of "321s") and 1 decimal for 1-60s range ("6.7s" instead of "6.70s")
- Exchange ID column shows last 8 chars with ellipsis prefix; full ID on hover, copies to clipboard on click

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/pages/Dashboard/Dashboard.tsx

@@ -1,4 +1,4 @@
-import { useState, useMemo, useCallback, useEffect } from 'react'
+import React, { useState, useMemo, useCallback, useEffect } from 'react'
 import { useParams, useNavigate, useSearchParams } from 'react-router'
 import { AlertTriangle, X, Search, Footprints, RotateCcw } from 'lucide-react'
 import {
@@ -113,7 +113,17 @@ function buildBaseColumns(): Column<Row>[] {
       header: 'Exchange ID',
       sortable: true,
       render: (_: unknown, row: Row) => (
-        <MonoText size="xs">{row.executionId}</MonoText>
+        <MonoText
+          size="xs"
+          title={row.executionId}
+          style={{ cursor: 'pointer' }}
+          onClick={(e: React.MouseEvent) => {
+            e.stopPropagation();
+            navigator.clipboard.writeText(row.executionId);
+          }}
+        >
+          ...{row.executionId.slice(-8)}
+        </MonoText>
       ),
     },
     {