BOM: confirm the plain Zero and Zero W as verified fallbacks

The BOM claimed "Zero W also works" as an aside. Checked it: Circle's
CHANGELOG gives gadget support for "Zero (2) (W)", the parentheses including
the plain Zero, and the README lists Raspberry Pi Zero as Tested with no
caveat. build.sh already emits kernel.img for RASPPI=1, and the MIDI gadget's
string descriptors are present in that image, so no build change is needed
for either board.

Keeping the Zero 2 W as the specified part on availability grounds. Records
that a plain Zero would permanently close the WiFi option in section 3a,
since it has no radio silicon at all.

Claude-Session: https://claude.ai/code/session_01TVCB25LBsmeteWvaSMz4Ne

PIANO-LED-CIRCLE-PLAN.md

@@ -162,7 +162,7 @@ is the first thing to settle, because it may close the option outright.
 
 | Item | Note |
 |---|---|
-| Raspberry Pi Zero 2 W | Zero W also works. Zero 2 W is current and quad-core. Headers not needed if the LED line is soldered. |
+| Raspberry Pi Zero 2 W | VERIFIED: the plain Zero and Zero W work too. `build.sh` already emits `kernel.img` for them, and the gadget's string descriptors are present in it, so either is a drop-in if Zero 2 W supply is a problem. Chosen anyway as the current and most available part; the quad core is headroom this workload does not need. Note a plain Zero would permanently close the WiFi option in section 3a. Headers not needed if the LED line is soldered. |
 | microSD card | Circle boots from FAT32. Tiny card is fine. |
 | WS2812B strip, 144 LEDs/m, 2m | Need 176 LEDs = 1.222m. Buy 2m, cut to length. |
 | 5V PSU, 6A | See the power note in section 7 before assuming this is enough. |