Phase 6: strip signature-restating docstrings; correct README/SETUP

- Collapsed Args:/Returns:/Raises: blocks that only restated the
  signature (364 lines): tektronix_base 48% -> ~20% doc density,
  helios_laser and uc480_camera likewise. Only docstrings whose entire
  body was those sections were touched.
- Preserved verbatim the comments that carry hardware knowledge the code
  can't express: uc480's USB split-transaction contention note (with its
  measured fps), the IS_ALLOW_STARTER_FW_UPLOAD segfault explanation, the
  QImage-copy rationale, and tektronix's NUMFRAMESACQuired warning.
- README: project structure, quick start, and every usage example now
  describe code that exists (they referenced hardware/bbd202.py,
  CoherentHOPSLaser, get_curve_binary, and 'python -m scanengine.app',
  none of which do). Added a headless-scan example and a read-a-scan-file
  example, since reuse without the GUI is the point of the refactor.
- SETUP: structure section defers to README instead of keeping a second
  stale copy; documents the vendored uEye SDK and the Genesis quarantine.
- ruff is now clean repo-wide: fixed the remaining raise-from, unused
  loop variables, placeholder f-strings, and a non-strict zip; the
  widget-layout semicolon idiom is an explicit config ignore rather than
  22 standing warnings.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

sc3_aui_app.py

@@ -13,7 +13,7 @@ from threading import Thread
 
 import numpy as np
 from PyQt6 import uic
-from PyQt6.QtCore import QObject, QThread, QTimer, Qt, pyqtSignal
+from PyQt6.QtCore import QThread, QTimer, Qt, pyqtSignal
 from PyQt6.QtGui import QImage, QPixmap
 from PyQt6.QtWidgets import (
     QApplication, QDialog, QDialogButtonBox, QFileDialog, QHBoxLayout, QLabel,