Software: pattern player, web page with a design library, GRBL tools

- python3 -m sandtable web: local web page to play designs from a library of
  27 built-in patterns, upload .thr or .svg, pause/skip/stop, jog and calibrate.
  Reconnects by itself when the USB cable comes back.
- Plays .thr files and built-in generators with an erase spiral between them,
  constant ball speed, host-side homing on stock GRBL 1.1 (Uno + CNC shield),
  FluidNC for the ESP32 board.
- Home switch guard: patterns never press the switch, so a press means lost
  steps and stops the machine at once with an alert.
- lineart.py turns SVG line drawings into one continuous path.
- Tests against a GRBL simulator.

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

software/.gitignore

@@ -0,0 +1,11 @@
+previews/*.gcode
+__pycache__/
+*.pyc
+.cache/
+removed-patterns/
+
+# fan art: trademarked logos and characters, for my own table only (not published)
+patterns/fan-art/
+art/fan-art/
+tools/make_fan_art.py
+previews/fan-art.png