Raspberry Pi Zero 2 W image builder; Power off/Restart buttons

pi/build-image.sh makes a ready-to-flash card: Raspberry Pi OS Lite 2026-10-06
+ the Gyre software as a service on http://gyre.local (port 80), first-boot
setup through cloud-init (user, SSH key, Wi-Fi, packages from the card), USB
host mode on the Zero 2's data port. No root: mtools for the boot partition,
debugfs for the root filesystem. Wi-Fi and credentials stay in the work dir.

Web page: Power off / Restart links when GYRE_POWER_BUTTONS=1 (set by the Pi
service); thumbnails keyed by file contents so pre-made ones ship on the card;
stale thumbnails pruned.

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

README.md

@@ -7,6 +7,7 @@ Gyre is a 12" kinetic sand table that draws patterns in sand. A steel ball rolls
 - `sand-table-v3.solidcraft`: the printable design (latest). Bodies named `REF_*` are bought parts, modeled for fit only. `sand-table-v2.solidcraft` is the previous version.
 - `print/v3/`: STL files for every printed part of the v3 build. **Use this set.** Print the two fit tests (`00`, `00b`) first. `print/README.md` has the parts list, print notes and assembly order; the older folders are kept for reference.
 - `software/`: the pattern player. Start it with `python3 -m sandtable web` for a web page with a library of designs; it drives the table from a computer over USB and erases between patterns. See `software/README.md`.
+- `pi/`: run Gyre on a Raspberry Pi Zero 2 W inside the table, with no computer needed: builds a ready-to-flash SD card image. See `pi/README.md`.
 - `pcb/`: an optional custom controller board (ESP32 + 2× DRV8825, FluidNC) that fits the Uno standoffs, with PCBWay order files. See `pcb/README.md`.
 - `sand-table-v2-assembly.step`: the v2 assembly, for viewing in any CAD tool.
 - `design-notes.md`: how it works, dimensions, parts to buy, hardware list and print settings.