Add recurring transaction detection, subscriptions page, and UK tax reporting

- Recurring service: auto-detects direct debits/subscriptions from CSV imports
  using frequency analysis; manual toggle in transaction detail drawer
- Subscriptions page (/subscriptions): groups recurring payments with monthly
  cost equivalents, next-payment badges, and re-scan trigger
- UK Tax page (/tax): payslips/P60 entry, income tax + NI + CGT + dividend tax
  calculations, configurable rate tables per tax year (pre-seeded 2024/25 and
  2025/26), editable in-app so Budget changes need no rebuild
- Migration 0006: tax_rate_configs, tax_profiles, payslips, manual_cgt_disposals
  with RLS; seeds 2025/2026 rate configs for existing users
- Chart tooltip fix: all Recharts tooltips now use TOOLTIP_STYLE constant so
  they render correctly across all dark/light themes

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

frontend/src/pages/investments/PortfolioCharts.tsx

@@ -10,6 +10,20 @@ const COLORS = [
   "#f59e0b","#8b5cf6","#06b6d4","#84cc16","#ef4444",
 ];
 
+const TOOLTIP_STYLE = {
+  contentStyle: {
+    background: "hsl(var(--card))",
+    border: "1px solid hsl(var(--border))",
+    borderRadius: "8px",
+    fontSize: "12px",
+    color: "hsl(var(--foreground))",
+    boxShadow: "0 4px 12px rgba(0,0,0,0.15)",
+  },
+  labelStyle: { color: "hsl(var(--foreground))", fontWeight: 500, marginBottom: "4px" },
+  itemStyle: { color: "hsl(var(--muted-foreground))" },
+  cursor: { fill: "hsl(var(--muted-foreground))", fillOpacity: 0.08 },
+};
+
 const TYPE_COLORS: Record<string, string> = {
   stock:  "#6366f1",
   etf:    "#22c55e",
@@ -181,16 +195,11 @@ export function CostVsValueChart({ portfolio }: { portfolio: PortfolioSummary })
             width={52}
           />
           <Tooltip
+            {...TOOLTIP_STYLE}
             formatter={(value: number, name: string) => [
               formatCurrency(value, portfolio.currency),
               name === "cost" ? "Cost basis" : "Current value",
             ]}
-            contentStyle={{
-              background: "hsl(var(--card))",
-              border: "1px solid hsl(var(--border))",
-              borderRadius: "8px",
-              fontSize: "12px",
-            }}
           />
           <Bar dataKey="cost" name="cost" fill="hsl(var(--muted-foreground))" opacity={0.4} radius={[4, 4, 0, 0]} barSize={20} />
           <Bar dataKey="value" name="value" radius={[4, 4, 0, 0]} barSize={20}>
@@ -265,13 +274,8 @@ export function ReturnChart({ portfolio }: { portfolio: PortfolioSummary }) {
           />
           <ReferenceLine x={0} stroke="hsl(var(--border))" strokeWidth={1.5} />
           <Tooltip
+            {...TOOLTIP_STYLE}
             formatter={(value: number) => [`${Number(value).toFixed(2)}%`, "Return"]}
-            contentStyle={{
-              background: "hsl(var(--card))",
-              border: "1px solid hsl(var(--border))",
-              borderRadius: "8px",
-              fontSize: "12px",
-            }}
           />
           <Bar dataKey="pct" radius={[0, 4, 4, 0]} barSize={18}>
             <LabelList