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>

hardware/t3r_protocol.py

@@ -193,14 +193,6 @@ def set_position(ch: int, position: int) -> bytes:
     return build_frame(CMD_SET_POSITION, struct.pack("<Bi", ch, position))
 
 
-def read_reg(ch: int, reg: int) -> bytes:
-    return build_frame(CMD_READ_REG, struct.pack("<BB", ch, reg))
-
-
-def write_reg(ch: int, reg: int, value: int) -> bytes:
-    return build_frame(CMD_WRITE_REG, struct.pack("<BBI", ch, reg, value))
-
-
 # ---------------------------------------------------------------------------
 # Response / event decoders. Each returns a dataclass (or None on bad length).
 # ---------------------------------------------------------------------------
@@ -261,13 +253,6 @@ class Position:
     position: int
 
 
-@dataclass
-class Reg:
-    ch: int
-    reg: int
-    value: int
-
-
 def decode_pong(p: bytes):
     if len(p) < 4:
         return None
@@ -304,13 +289,6 @@ def decode_position(p: bytes):
     return Position(ch, pos)
 
 
-def decode_reg(p: bytes):
-    if len(p) < 6:
-        return None
-    ch, reg, value = struct.unpack_from("<BBI", p, 0)
-    return Reg(ch, reg, value)
-
-
 def decode_event_position(p: bytes):
     """MOTION_DONE / STOPPED share the (ch, position) layout."""
     return decode_position(p)