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/api/v1/transactions.py

@@ -611,6 +611,18 @@ async def import_transactions(
     return result
 
 
+@router.post("/detect-recurring")
+async def detect_recurring_endpoint(
+    db: AsyncSession = Depends(get_db),
+    user=Depends(get_current_user),
+):
+    """Manually trigger recurring transaction detection for the current user."""
+    from app.services.recurring_service import detect_recurring
+    result = await detect_recurring(db, user.id)
+    await db.commit()
+    return result
+
+
 @router.get("/import/template")
 async def import_template():
     from fastapi.responses import Response