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>

docs/genesis_verification.md

@@ -0,0 +1,25 @@
+# Genesis laser — hardware verification checklist
+
+`hardware/genesis_core.py` was extracted from `tools/genesis_laser_gui.py`,
+but the extraction changed behavior in ways only the bench can adjudicate.
+Until every row below is resolved, **both files stay in the repo unchanged**:
+`genesis_laser_gui.py` is the reference implementation, `genesis_core.py`
+(+ `tools/genesis_laser_control.py`) is the intended successor.
+
+Run these with the Genesis laser connected, interlock chain accessible, and
+a front-panel/manual reference for current and temperature readouts.
+
+| # | Divergence | Bench test | Resolution |
+|---|---|---|---|
+| 1 | **ADS7828 command byte.** Reference passes raw command bytes (`0x84`, `0xe4`, `0x94` — `genesis_laser_gui.py:73-77`); core synthesizes `0x80 \| (ch<<4) \| 0x0c` → `0x8C` for ch0 (`genesis_core.py:413`), different PD1/PD0 power-down bits. | Read the same ADC channel through both implementations; compare against the front-panel current readout. Also check for settling differences right after power-up. | Keep whichever matches the panel; fix the other. |
+| 2 | **LDD enable polarity.** Reference `get_ldd_enable()` returns `not bool(value & 0x01)` ("Inverted logic", `genesis_laser_gui.py:602-612`); core returns the un-inverted bit (`genesis_core.py:585-599`). Same register, opposite answers. | With emission verifiably OFF (keyswitch off), read LDD status via both. Exactly one will say "disabled". | Adopt the polarity that matches reality; document the register semantics inline. |
+| 3 | **Shutter: manual or bit-controlled?** Reference docs say "this laser has a MANUAL shutter" and `emergency_stop()` deliberately leaves it alone; core `set_shutter()` toggles a PCA9555 bit and `emergency_stop()`/`enter_safe_state()` rely on it. | Toggle `set_shutter()` from core with the beam blocked; observe whether anything physical actuates. | If the bit is inert, remove `set_shutter` and fix the safe-state functions; if real, correct the `tools/` docs. |
+| 4 | **ADC filtering dropped.** Reference reads 3× and takes median (`i2c_read_discard_high_low`, `genesis_laser_gui.py:341-364`) or retries until two reads agree; core does single unfiltered reads. | Log ~100 consecutive current readings through core; if the spread is more than display noise, filtering was load-bearing. | Port the median-of-3 helper into `genesis_core.I2CProtocol`. |
+| 5 | **Scaling dropped.** Reference converts to Amps/Watts (`AMPS_FULLSCALE * ADC_TO_VOLTS`); core returns raw 0–4095 counts. | Compare a scaled reading against the front panel. | Port the scaling constants + conversion into core. |
+| 6 | **Temperatures + power monitoring dropped.** `get_main_temp` / `get_etalon_temp` / `get_shg_temp` / `get_power_actual` exist only in the reference. | Confirm each channel's reading is sane vs. front panel. | Port the four getters into core. |
+| 7 | **`pre_flight_check()` dropped.** Reference validates remote-enable + keyswitch + interlock before emission. | n/a — code review + one interlock-open test. | Port into core; call it from `genesis_laser_control.py` before enabling. |
+
+When all rows are resolved: port the verified behavior into
+`genesis_core.py`, update `tools/genesis_laser_control.py`, delete
+`tools/genesis_laser_gui.py`, and remove this checklist plus the warning
+header in `genesis_core.py`.