chore: replace Unicode/emoji icons with Lucide React

Adds lucide-react and replaces all HTML entity and emoji icons across
the UI with proper SVG icon components. Tree-shaken — only imported
icons are bundled.

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

ui/src/pages/AgentHealth/AgentHealth.tsx

@@ -1,5 +1,6 @@
 import { useState, useMemo, useCallback } from 'react';
 import { useParams, useNavigate } from 'react-router';
+import { ExternalLink, RefreshCw, Pencil } from 'lucide-react';
 import {
   StatCard, StatusDot, Badge, MonoText, ProgressBar,
   GroupCard, DataTable, LineChart, EventFeed, DetailPanel,
@@ -357,7 +358,7 @@ export default function AgentHealth() {
               navigate(`/agents/${row.application}/${row.id}`);
             }}
           >
-            ↗
+            <ExternalLink size={14} />
           </button>
         ),
       },
@@ -621,7 +622,7 @@ export default function AgentHealth() {
                 <span className={styles.configLabel}>Metrics</span>
                 <Badge label={appConfig.metricsEnabled ? 'On' : 'Off'} color={appConfig.metricsEnabled ? 'success' : 'error'} variant="filled" />
               </div>
-              <button className={styles.configEditBtn} title="Edit config" onClick={startConfigEdit}>&#x270E;</button>
+              <button className={styles.configEditBtn} title="Edit config" onClick={startConfigEdit}><Pencil size={14} /></button>
             </>
           )}
         </div>
@@ -695,7 +696,7 @@ export default function AgentHealth() {
                 {logSortAsc ? '\u2191' : '\u2193'}
               </button>
               <button className={styles.refreshBtn} onClick={() => setLogRefreshTo(new Date().toISOString())} title="Refresh">
-                &#x21bb;
+                <RefreshCw size={14} />
               </button>
             </div>
           </div>
@@ -745,7 +746,7 @@ export default function AgentHealth() {
                 {eventSortAsc ? '\u2191' : '\u2193'}
               </button>
               <button className={styles.refreshBtn} onClick={() => setEventRefreshTo(new Date().toISOString())} title="Refresh">
-                &#x21bb;
+                <RefreshCw size={14} />
               </button>
             </div>
           </div>