fix(lint): auto-fix ruff violations and tune lint rules

- Auto-fixed 4,496 lint issues (import sorting, modern syntax, etc.)
- Added ignore rules for patterns intentional in this codebase:
  E402 (late imports), E712 (SQLAlchemy filters), B904 (raise from),
  SIM108/SIM105/SIM117 (readability preferences)
- Added per-file ignores for tests and scripts
- Excluded broken scripts/rename_terminology.py (has curly quotes)

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

tests/unit/utils/test_vat.py

@@ -3,12 +3,9 @@
 
 from decimal import Decimal
 
-import pytest
-
 from app.utils.vat import (
     EU_VAT_RATES,
     VATRegime,
-    VATResult,
     calculate_vat_amount,
     determine_vat_regime,
     get_vat_rate_for_country,