Phase 2: Better reporting UI with charts and exports

- Add CSV export utility for ledger data (generateLedgerCSV)
- Export formatters: pence to pounds, proper CSV escaping
- Date range filtering (from/to inputs) on reports page
- Export CSV button with proper formatting for accountants
- New \"Trends\" tab with visual profit trend chart
- SVG bar chart shows last 12 months of profit
- Charts color-coded: green (profit), red (loss)
- Shows monthly values and best/worst month stats
- Export functionality:
  - Filters by date range
  - Combines all income sources (orders + manual sales)
  - Includes COGS (purchases) and expenses
  - Generates PDF-ready CSV with summary rows
  - Downloads with proper date-stamped filename

CSV exports are formatted for accountants and tax software:
- Includes summary totals
- Proper date formatting (DD/MM/YYYY)
- Escaped descriptions for safe import
- Clear categorization

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/lib/csvExport.ts

@@ -0,0 +1,122 @@
+/**
+ * Export financial data as CSV for accountants
+ */
+
+interface LedgerRow {
+  date: Date;
+  type: 'INCOME' | 'EXPENSE';
+  description: string;
+  amount: number; // pence
+  category?: string;
+}
+
+/**
+ * Convert pence to pounds string (e.g., 5000 -> "50.00")
+ */
+export function penceToPounds(pence: number): string {
+  return (pence / 100).toFixed(2);
+}
+
+/**
+ * Generate CSV from ledger data
+ */
+export function generateLedgerCSV(rows: LedgerRow[], title: string): string {
+  const lines: string[] = [];
+
+  // Header
+  lines.push(`${title}`);
+  lines.push(`Generated: ${new Date().toISOString().split('T')[0]}`);
+  lines.push('');
+
+  // Column headers
+  lines.push('Date,Type,Description,Category,Amount (£)');
+
+  // Data rows
+  const sortedRows = [...rows].sort((a, b) => b.date.getTime() - a.date.getTime());
+  for (const row of sortedRows) {
+    const dateStr = row.date.toLocaleDateString('en-GB', {
+      year: 'numeric',
+      month: '2-digit',
+      day: '2-digit',
+    });
+    const amountStr = penceToPounds(row.amount);
+    const category = row.category || '';
+
+    // Escape quotes in description
+    const description = `"${row.description.replace(/"/g, '""')}"`;
+
+    lines.push(`${dateStr},${row.type},${description},${category},${amountStr}`);
+  }
+
+  // Summary
+  lines.push('');
+  const totalIncome = rows
+    .filter((r) => r.type === 'INCOME')
+    .reduce((sum, r) => sum + r.amount, 0);
+  const totalExpense = rows
+    .filter((r) => r.type === 'EXPENSE')
+    .reduce((sum, r) => sum + r.amount, 0);
+  const profit = totalIncome - totalExpense;
+
+  lines.push(`TOTAL INCOME,,,${penceToPounds(totalIncome)}`);
+  lines.push(`TOTAL EXPENSES,,,${penceToPounds(totalExpense)}`);
+  lines.push(`NET PROFIT,,,${penceToPounds(profit)}`);
+
+  return lines.join('\n');
+}
+
+/**
+ * Generate CSV of audit changes for compliance
+ */
+export interface AuditRow {
+  date: Date;
+  action: string;
+  entity: string;
+  id: string;
+  amount?: number;
+  changedBy: string;
+  reason?: string;
+}
+
+export function generateAuditCSV(rows: AuditRow[]): string {
+  const lines: string[] = [];
+
+  lines.push('Financial Audit Trail');
+  lines.push(`Generated: ${new Date().toISOString().split('T')[0]}`);
+  lines.push('');
+
+  lines.push('Date,Time,Action,Entity Type,Entity ID,Amount (£),Changed By,Reason');
+
+  const sortedRows = [...rows].sort((a, b) => b.date.getTime() - a.date.getTime());
+  for (const row of sortedRows) {
+    const dateStr = row.date.toLocaleDateString('en-GB', {
+      year: 'numeric',
+      month: '2-digit',
+      day: '2-digit',
+    });
+    const timeStr = row.date.toLocaleTimeString('en-GB', {
+      hour: '2-digit',
+      minute: '2-digit',
+      second: '2-digit',
+    });
+    const amountStr = row.amount ? penceToPounds(row.amount) : '';
+    const reason = `"${(row.reason || '').replace(/"/g, '""')}"`;
+
+    lines.push(
+      `${dateStr},${timeStr},${row.action},${row.entity},${row.id},${amountStr},${row.changedBy},${reason}`
+    );
+  }
+
+  return lines.join('\n');
+}
+
+/**
+ * Trigger browser download of CSV file
+ */
+export function downloadCSV(csv: string, filename: string) {
+  const blob = new Blob([csv], { type: 'text/csv;charset=utf-8;' });
+  const link = document.createElement('a');
+  link.href = URL.createObjectURL(blob);
+  link.download = filename;
+  link.click();
+}