Add ruff CI gate and fix deterministic lint issues

Introduces pyproject.toml + .github/workflows/ruff.yml that gate
E701, E711, E712, F401, F541 on every PR and push to main.

Fixes the existing findings for those rules:
- Remove unused imports (sklearn.silhouette_score, numpy in several
  files, typing.Optional, get_one_face, gpu_cvt_color, sys,
  insightface.face_align)
- Annotate the intentional tkinter_fix side-effect import with
  `# noqa: F401`
- Split multi-statement `if x: y` one-liners onto separate lines
- Replace `state == True` / `state == False` with truthiness checks
- Drop `f` prefix from f-strings with no placeholders

F841 (unused-variable), E402 (module-level-import-not-at-top), and
F821 (undefined-name) are left out of the gate for now — they surface
real findings (including a latent NameError in face_swapper.py) that
require human review to fix safely.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

modules/gpu_processing.py

@@ -21,7 +21,7 @@ from __future__ import annotations
 import os
 import cv2
 import numpy as np
-from typing import Tuple, Optional
+from typing import Tuple
 
 # ---------------------------------------------------------------------------
 # CUDA availability detection (evaluated once at import time)