feat: migrate all icons to Lucide React

Replace unicode characters, emoji, and inline SVGs with lucide-react
components across the entire design system and page layer. Update
tests to assert on SVG elements instead of text content.

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

src/pages/Dashboard/Dashboard.tsx

@@ -1,5 +1,6 @@
-import { useState, useMemo } from 'react'
+import React, { useState, useMemo } from 'react'
 import { useParams, useNavigate } from 'react-router-dom'
+import { TrendingUp, TrendingDown, ArrowRight, ExternalLink, AlertTriangle } from 'lucide-react'
 import styles from './Dashboard.module.css'
 
 // Layout
@@ -43,10 +44,10 @@ const ACCENT_TO_COLOR: Record<KpiMetric['accent'], string> = {
   warning: 'var(--warning)',
 }
 
-const TREND_ICONS: Record<KpiMetric['trend'], string> = {
-  up: '\u2191',
-  down: '\u2193',
-  neutral: '\u2192',
+const TREND_ICONS: Record<KpiMetric['trend'], React.ReactNode> = {
+  up: <TrendingUp size={12} />,
+  down: <TrendingDown size={12} />,
+  neutral: <ArrowRight size={12} />,
 }
 
 function sentimentToVariant(sentiment: KpiMetric['trendSentiment']): 'success' | 'error' | 'muted' {
@@ -60,7 +61,7 @@ function sentimentToVariant(sentiment: KpiMetric['trendSentiment']): 'success' |
 const kpiItems: KpiItem[] = kpiMetrics.map((m) => ({
   label: m.label,
   value: m.unit ? `${m.value} ${m.unit}` : m.value,
-  trend: { label: `${TREND_ICONS[m.trend]} ${m.trendValue}`, variant: sentimentToVariant(m.trendSentiment) },
+  trend: { label: <><span style={{ display: 'inline-flex', verticalAlign: 'middle' }}>{TREND_ICONS[m.trend]}</span> {m.trendValue}</>, variant: sentimentToVariant(m.trendSentiment) },
   subtitle: m.detail,
   sparkline: m.sparkline,
   borderColor: ACCENT_TO_COLOR[m.accent],
@@ -206,7 +207,7 @@ export function Dashboard() {
             navigate(`/exchanges/${row.id}`)
           }}
         >
-          &#x2197;
+          <ExternalLink size={14} />
         </button>
       ),
     }
@@ -303,7 +304,7 @@ export function Dashboard() {
                 className={styles.openDetailLink}
                 onClick={() => navigate(`/exchanges/${selectedExchange.id}`)}
               >
-                Open full details &#x2192;
+                Open full details <ArrowRight size={14} style={{ verticalAlign: 'middle' }} />
               </button>
             </div>
 
@@ -428,7 +429,7 @@ export function Dashboard() {
             expandedContent={(row) =>
               row.errorMessage ? (
                 <div className={styles.inlineError}>
-                  <span className={styles.inlineErrorIcon}>⚠</span>
+                  <span className={styles.inlineErrorIcon}><AlertTriangle size={14} /></span>
                   <div>
                     <div className={styles.inlineErrorText}>{row.errorMessage}</div>
                     <div className={styles.inlineErrorHint}>Click to view full stack trace</div>