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>

helios_test_app.py

@@ -6,15 +6,13 @@ Simple PyQt6 GUI for testing and controlling the Helios laser.
 
 import sys
 import logging
-from typing import Optional
-from enum import Enum
 
 from PyQt6.QtWidgets import (
     QApplication, QMainWindow, QWidget, QVBoxLayout, QHBoxLayout,
     QGroupBox, QLabel, QLineEdit, QPushButton, QComboBox, QSpinBox,
-    QStatusBar, QMessageBox, QTabWidget, QTextEdit
+    QMessageBox, QTabWidget, QTextEdit
 )
-from PyQt6.QtCore import Qt, QThread, pyqtSignal, QObject
+from PyQt6.QtCore import QThread, pyqtSignal, QObject
 from PyQt6.QtGui import QFont
 
 from hardware.helios_laser import HeliosLaser, PulseMode