Controller board: ESP32 + 2x StepStick carrier (v0.4), FluidNC config

- KiCad project generated by pcb/tools (design, route, schematic, fab outputs).
- v0.4 fixes the v0.3 review findings: low-dropout 3.3 V regulator, OR'd 5 V
  supply, polyfuse, USB ESD protection, input clamps, ceramic decoupling at the
  drivers, A4988/DRV8825 jumper, ground stitching. DRC/ERC clean.
- v0.3 (as ordered) kept in pcb/archive/v0.3.
- FluidNC config.yaml for the board; rho hard limit on.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

pcb/tools/place_check.py

@@ -0,0 +1,21 @@
+"""Build the board, report placement problems and write an unrouted PCB for a look."""
+import os
+import sys
+
+sys.path.insert(0, os.path.dirname(__file__))
+import design as D
+from board import build, check_placement, write_pcb, write_project, keepout_zone
+
+OUT = os.path.expanduser('~/kicad/sandtable-controller')
+
+parts = build()
+probs = check_placement(parts)
+print(f'{len(parts)} parts, {sum(len(v) for v in D.NETS.values())} net pins, {len(D.NETS)} nets')
+for p in probs:
+    print('  !', p)
+if not probs:
+    print('  placement OK')
+zones = [keepout_zone('ANTENNA', 18.75, 56.9, 67.25, D.BOARD_H)]
+write_pcb(os.path.join(OUT, 'sandtable-controller.kicad_pcb'), parts, zones=zones)
+write_project(os.path.join(OUT, 'sandtable-controller.kicad_pro'), 'sandtable-controller')
+print('wrote unrouted board')