Phase 1c: prune remaining dead functions, unused imports, quarantine Genesis

- uc480_camera: drop never-called _capture_paused/get_framerate (the
  hardware question _capture_paused encoded is now in KNOWN_ISSUES.md)
- t3r_protocol: drop read_reg/write_reg/decode_reg/Reg (commands never
  wired into the driver)
- bbd20x: drop _update0x0212 (never dispatched) and 8 of 9 unused
  trigger convenience wrappers; apt_constants: drop TriggerBitsStepper
  (servo-only rig)
- ruff --fix: 35 unused imports across all apps; drop unused T3R_BAUD
- genesis_core.py: quarantine warning header; docs/genesis_verification.md
  bench checklist for the 7 divergences vs tools/genesis_laser_gui.py

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

sc3_aui_app.py

@@ -16,10 +16,9 @@ import threading
 from threading import Thread
 
 import numpy as np
-import serial
 from PyQt6 import uic
 from PyQt6.QtCore import QObject, QThread, QTimer, Qt, pyqtSignal, pyqtSlot
-from PyQt6.QtGui import QImage, QPixmap, QPainter, QColor, QPen
+from PyQt6.QtGui import QImage, QPixmap
 from PyQt6.QtWidgets import (
     QApplication, QDialog, QDialogButtonBox, QFileDialog, QHBoxLayout, QLabel,
     QListWidget, QListWidgetItem, QMainWindow, QMessageBox, QPushButton,
@@ -93,7 +92,6 @@ SCAN_RAMP_MM        = SCAN_VELOCITY_MM_S**2 / (2.0 * SCAN_ACCEL_MM_S2)
 SCAN_RAMP_BUFFER_MM = 1.0
 SCOPE_SAMPLE_RATE   = 6.25e9    # 6.25 GS/s → 160 ps/sample
 SCOPE_TRIG_LEVEL_V  = 0.500
-T3R_BAUD            = 115200
 
 # GR-axis rotation defaults (used by ScanWorker between angles)
 GR_MICROSTEPS       = 8         # microsteps/full-step on GR axis (ch3)