feat: add theme-aware chart colors for dark/light mode support

Replace hardcoded dark-theme hex colors in recharts components
(tooltips, axes) with a useChartTheme hook that reads the current
theme from ThemeContext. Charts now render correctly in both light
and dark mode.

Closes leeworks-agents/SPARC#1324

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

frontend/src/pages/Batch.tsx

@@ -3,6 +3,7 @@ import { useMutation, useQuery } from '@tanstack/react-query';
 import { analysisApi } from '../api/client';
 import { Rocket, CheckCircle, AlertCircle, ChevronDown, ChevronUp, RefreshCw, Inbox } from 'lucide-react';
 import { BarChart, Bar, XAxis, YAxis, Tooltip, ResponsiveContainer, Cell } from 'recharts';
+import { useChartTheme } from '../context/useChartTheme';
 import type { BatchAnalysisResult } from '../types';
 
 export function Batch() {
@@ -12,6 +13,8 @@ export function Batch() {
   const [result, setResult] = useState<BatchAnalysisResult | null>(null);
   const [expandedItems, setExpandedItems] = useState<Set<string>>(new Set());
 
+  const chartTheme = useChartTheme();
+
   const modelsQuery = useQuery({
     queryKey: ['models'],
     queryFn: () => analysisApi.listModels(),
@@ -210,15 +213,11 @@ export function Batch() {
             <div className="bg-bg-card/60 border border-primary/15 rounded-2xl p-6">
               <ResponsiveContainer width="100%" height={300}>
                 <BarChart data={chartData}>
-                  <XAxis dataKey="name" stroke="#94a3b8" fontSize={12} />
-                  <YAxis stroke="#94a3b8" fontSize={12} />
+                  <XAxis dataKey="name" stroke={chartTheme.axisStroke} fontSize={12} />
+                  <YAxis stroke={chartTheme.axisStroke} fontSize={12} />
                   <Tooltip
-                    contentStyle={{
-                      backgroundColor: '#1e293b',
-                      border: '1px solid rgba(99, 102, 241, 0.3)',
-                      borderRadius: '8px',
-                    }}
-                    labelStyle={{ color: '#f8fafc' }}
+                    contentStyle={chartTheme.tooltipContentStyle}
+                    labelStyle={chartTheme.tooltipLabelStyle}
                   />
                   <Bar dataKey="patents" radius={[4, 4, 0, 0]}>
                     {chartData.map((entry, index) => (