feat(uno-q): flash-sketch helper + matrix_rain as the board boot default

- flash-sketch.sh: compile + flash a sketch dir onto a board's MCU over adb
  (push → arduino-cli compile with TMPDIR=/tmp → arduino-flash @ 0x80F0000).
  Defaults to sketches/matrix_rain; includes a fleet loop over adb devices.
  DRYs up the recipe and makes "set the board default" one command.
- Designate matrix_rain as the boot animation boards ship with (the flashed
  MCU sketch persists across power cycles). Documented in the sketches README
  + parent Files list.

Flashed matrix_rain to the board via the helper (821 bytes, verified E2E).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

deploy/uno-q/README.md

@@ -191,6 +191,8 @@ cloud-with-fallback. In APESS, the team's provider/fallback toggle picks the ali
 - `provision-fleet.sh` — host: provision a whole fleet from `fleet.csv` (env + self-register + timer/cron).
 - `fleet.csv.example` — kit→adb-serial assignment template for `provision-fleet.sh`.
 - `gen-qr-sheet.sh` — host: render the sticker CSV into a self-contained printable QR sheet (needs `qrencode`).
+- `flash-sketch.sh` — host: compile + flash a sketch onto a board's MCU (sets the boot animation; default `sketches/matrix_rain`).
+- `sketches/` — LED-matrix animations (`matrix_rain` is the board default; `matrix_effects` is a sampler). See `sketches/README.md`.
 - `apess-selfregister.sh` — on-board: announce into APESS's unclaimed pool on boot.
 - `apess-node.env.example` — per-board onboarding identity (KIT_ID / CLAIM_CODE / FLEET_SECRET / APESS_URL).
 - `systemd/*.service` + `apess-selfregister.timer` — production units (need root).

deploy/uno-q/flash-sketch.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+# Compile + flash an Arduino sketch onto an Uno Q's MCU over adb. The sketch is
+# written to MCU flash (0x80F0000) and runs on every boot/reset — so this is how
+# you set a board's default ("boot") animation. Attendees overwrite it when they
+# flash their own sketch during the workshop; re-run this to restore the default.
+#
+#   ./flash-sketch.sh <adb-serial> [sketch-dir]
+#   ./flash-sketch.sh 65301572                       # defaults to the boot animation
+#   ./flash-sketch.sh 65301572 sketches/matrix_effects
+#
+# Fleet-wide (restore the default on every connected board):
+#   for s in $(adb devices | awk 'NR>1 && $2=="device"{print $1}'); do ./flash-sketch.sh "$s"; done
+set -euo pipefail
+
+HERE="$(cd "$(dirname "$0")" && pwd)"
+S="${1:?usage: flash-sketch.sh <adb-serial> [sketch-dir]}"
+# The designated board default (boot animation).
+SKETCH_DIR="${2:-$HERE/sketches/matrix_rain}"
+NAME="$(basename "$SKETCH_DIR")"
+[ -r "$SKETCH_DIR/$NAME.ino" ] || { echo "no $SKETCH_DIR/$NAME.ino" >&2; exit 1; }
+
+REMOTE="/home/arduino/sketches/$NAME"
+
+echo "==> [$S] push $NAME"
+adb -s "$S" shell 'mkdir -p /home/arduino/sketches' >/dev/null
+adb -s "$S" push "$SKETCH_DIR" /home/arduino/sketches/ >/dev/null
+
+echo "==> [$S] compile (TMPDIR=/tmp dodges the adb shell's /data/local/tmp)"
+adb -s "$S" shell "cd $REMOTE && TMPDIR=/tmp arduino-cli compile --fqbn arduino:zephyr:unoq --export-binaries . 2>&1 | tail -3"
+
+echo "==> [$S] flash (OpenOCD @ 0x80F0000)"
+adb -s "$S" shell "BIN=\$(ls $REMOTE/build/arduino.zephyr.unoq/*.elf-zsk.bin 2>/dev/null | head -1); \
+  [ -n \"\$BIN\" ] || { echo 'no .elf-zsk.bin — compile failed' >&2; exit 1; }; \
+  /usr/local/bin/arduino-flash \"\$BIN\" 2>&1 | tail -3"
+
+echo "==> [$S] done — $NAME flashed and running"

deploy/uno-q/sketches/README.md

@@ -6,9 +6,23 @@ Animations for the Arduino Uno Q's built-in **13×8 monochrome blue** LED matrix
 
 | Sketch | What it does |
 |--------|--------------|
-| `matrix_rain/` | Digital "rain" — per-column drops (head + short trail) at staggered speeds. |
+| `matrix_rain/` | Digital "rain" — per-column drops (head + short trail) at staggered speeds. **The board default** (boot animation). |
 | `matrix_effects/` | Sampler that cycles rain → knight-rider → comet → ripple → bloom → breathe → sparkle → checker → wipe. |
 
+## The board default (boot animation)
+
+`matrix_rain` is the designated default a board shows on boot. The flashed sketch
+lives in MCU flash and runs on every power-up, so setting the default is just
+flashing it. Attendees overwrite it when they flash their own sketch during the
+workshop; re-run `flash-sketch.sh` to restore it afterward.
+
+```sh
+../flash-sketch.sh <adb-serial>                 # flashes matrix_rain (the default)
+../flash-sketch.sh <adb-serial> matrix_effects  # or any sketch dir
+# restore the default on every connected board:
+for s in $(adb devices | awk 'NR>1 && $2=="device"{print $1}'); do ../flash-sketch.sh "$s"; done
+```
+
 ## How they work
 
 The matrix API is intentionally tiny: `matrix.begin()` and