Add WonderSwan cartridge organizer

hardware/wonderswan-cartridge-organizer/README.md

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+# WonderSwan 3×3 cartridge organizer
+
+This is a support-free, stepped display organizer for nine standard Bandai
+WonderSwan cartridges. Three continuous rails hold three cartridges each, and
+low divider ribs keep the cartridges aligned without covering their labels.
+
+## Researched cartridge envelope
+
+The model uses a nominal cartridge envelope of **65.2 mm wide × 41.8 mm high ×
+6.0 mm thick**. The dimensions come from a Japanese WonderSwan hardware listing
+that specifies the cassette as 41.8 × 65.2 × 6.0 mm. The Ritsumeikan Center for
+Game Studies independently catalogs a physical WonderSwan cartridge at 4.1 ×
+6.6 × 0.6 cm.
+
+- [Media World WonderSwan specifications](https://mediaworld.co.jp/products/10011140001)
+- [RCGS physical-package record](https://collection.rcgs.jp/page/PACKAGE0005000)
+
+The 6.0 mm thickness is the critical fit dimension. The default rail is 6.8 mm
+wide, providing 0.4 mm nominal clearance on each face. Because vintage shells,
+reproduction shells, and individual FDM printers can vary, print the clearance
+coupon before printing the full organizer.
+
+## Included files
+
+- `wonderswan-organizer-3x3.stl` — ready-to-slice nine-cartridge organizer
+- `wonderswan-slot-clearance-test.stl` — small fit test with 6.4, 6.8, and
+  7.2 mm channels, ordered from front to back
+- `wonderswan-organizer.scad` — editable OpenSCAD source
+- `generate.py` — parameterized STL and preview generator
+- `wonderswan-organizer-preview.png` — rendered scale preview with cartridge
+  placeholders
+
+Default organizer dimensions: **207.6 × 57.8 × 47.0 mm**. It fits diagonally or
+straight on most nominal 220 × 220 mm beds; check the slicer's printable-area
+margin before starting the job.
+
+## First test and printing
+
+1. Print `wonderswan-slot-clearance-test.stl` base-down.
+2. Try an expendable cartridge in the three channels. They are 6.4, 6.8, and
+   7.2 mm from the coupon's front edge to its back edge.
+3. Use the narrowest channel that inserts smoothly without scraping or bowing
+   the walls.
+4. If 6.8 mm fits, print the supplied organizer STL. Otherwise change
+   `slot_width` in the OpenSCAD file or regenerate the STL with `--slot-width`.
+
+Suggested starting settings:
+
+- PLA or PETG
+- 0.20 mm layer height
+- 3 perimeters
+- 15% gyroid or grid infill
+- Base flat on the build plate
+- No supports
+- A 5–8 mm brim if the printer tends to lift long parts
+
+## Regenerating the STL
+
+The OpenSCAD source is the simplest route. For scripted generation:
+
+```sh
+python3 -m venv .venv
+.venv/bin/pip install trimesh shapely mapbox-earcut manifold3d matplotlib
+.venv/bin/python generate.py --columns 3 --rows 3 --slot-width 6.8
+```
+
+Changing the number of columns changes the bed-width requirement. For a common
+220 mm bed, three columns is the practical maximum at full cartridge width.