chore: lint and format entire codebase

Run ruff check --fix: remove unused imports (F401), fix f-strings
without placeholders (F541), remove unused variables (F841), fix
duplicate dict key (F601).

Run isort --profile black: normalize import ordering across all files.

Run ruff format: apply consistent formatting (black-compatible) to
all 58 Python files.

3 intentional E402 remain (imports after require_yaml() must execute
after yaml is available).

scripts/sect233r1.py

@@ -9,6 +9,7 @@ Curve: sect233r1 (NIST B-233, SEC 2 v2)
 Field: GF(2^233) with irreducible polynomial t^233 + t^74 + 1
 Equation: y^2 + xy = x^3 + x^2 + b
 """
+
 from __future__ import annotations
 
 import hashlib
@@ -34,6 +35,7 @@ _H = 2
 
 # GF(2^233) field arithmetic
 
+
 def _gf_reduce(a: int) -> int:
     """Reduce polynomial a modulo t^233 + t^74 + 1."""
     while a.bit_length() > _M:
@@ -171,6 +173,7 @@ def _ec_mul(k: int, p: tuple[int, int] | None) -> tuple[int, int] | None:
 
 # ECDSA-SHA256 verification
 
+
 def _modinv(a: int, m: int) -> int:
     """Modular inverse of a modulo m (integers, not GF(2^m))."""
     if a < 0: