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>

backend/app/db/models/__init__.py

@@ -11,9 +11,11 @@ from app.db.models.investment_transaction import InvestmentTransaction
 from app.db.models.currency import Currency, ExchangeRate
 from app.db.models.net_worth_snapshot import NetWorthSnapshot
 from app.db.models.audit_log import AuditLog
+from app.db.models.tax import TaxRateConfig, TaxProfile, Payslip, ManualCGTDisposal
 
 __all__ = [
     "User", "Session", "Account", "Category", "Transaction", "Budget",
     "Asset", "AssetPrice", "InvestmentHolding", "InvestmentTransaction",
     "Currency", "ExchangeRate", "NetWorthSnapshot", "AuditLog",
+    "TaxRateConfig", "TaxProfile", "Payslip", "ManualCGTDisposal",
 ]