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/schemas/transaction.py

@@ -35,6 +35,8 @@ class TransactionUpdate(BaseModel):
     merchant: str | None = None
     notes: str | None = None
     tags: list[str] | None = None
+    is_recurring: bool | None = None
+    recurring_rule: dict | None = None
 
 
 class TransactionFilter(BaseModel):
@@ -71,6 +73,7 @@ class TransactionResponse(BaseModel):
     notes: str | None
     tags: list[str]
     is_recurring: bool
+    recurring_rule: dict | None = None
     attachment_refs: list[dict] = []
     created_at: datetime
     updated_at: datetime