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/components/layout/Sidebar.tsx

@@ -13,15 +13,19 @@ import {
   ChevronLeft,
   ChevronRight,
   Coins,
+  Repeat,
+  Receipt,
 } from "lucide-react";
 
 const navItems = [
   { href: "/", icon: LayoutDashboard, label: "Dashboard" },
   { href: "/accounts", icon: CreditCard, label: "Accounts" },
   { href: "/transactions", icon: ArrowLeftRight, label: "Transactions" },
+  { href: "/subscriptions", icon: Repeat, label: "Subscriptions" },
   { href: "/budgets", icon: PiggyBank, label: "Budgets" },
   { href: "/investments", icon: TrendingUp, label: "Investments" },
   { href: "/reports", icon: BarChart3, label: "Reports" },
+  { href: "/tax", icon: Receipt, label: "Tax" },
   { href: "/predictions", icon: Sparkles, label: "Predictions" },
   { href: "/settings", icon: Settings, label: "Settings" },
 ];