Coaster v0.2.1

Final release of the v0.2 board line. The hardware design has moved on to v0.3 (see pcb/ on main), so this release wraps up everything needed to build, flash, and print the v0.2 coaster.

Changes since v0.2.0

• Firmware: long-press brown-out fix — the show now plays only on a true power-on reset (PORF), making a worn-battery reset-relight loop impossible, with a soft-start settle phase so a cell depressed by a long press recovers before the bright phase.
• Enclosure: first release of the 3D-printed shell. The FreeCAD source (enclosure/coaster.FCStd) is now in the tree with a headless STEP/STL export build (make -C enclosure build).

Assets

Asset	Notes
coaster-v0.2.1-firmware.hex	ATtiny13A, 282 bytes. Fuses: lfuse=0x6A, hfuse=0xFD (1.8V BOD). Flashing recipe and gotchas in the README at this tag
coaster-v0.2.1-schematic.{svg,png}	Schematic renderings of the v0.2 board
coaster-v0.2.1-schematic.net	Protel netlist (canonical machine-readable circuit)
coaster-v0.2.1-{top,bottom,shield}.stl	3D printing assets: spiral-flexure lid, PCB tray, thin insert between PCB and lid
coaster-v0.2.1-{top,bottom,shield}.step	Same bodies as STEP, for CAD interference checks

The schematic assets describe the v0.2 board and are carried over from tag v0.2.0 (the v0.2 EasyEDA design source lives in the tree at that tag); the pcb/ directory at this tag already contains the in-development v0.3 KiCad design.