feat(vapor): add Playdate simulator target

[doodlewind]

Summary

• add a playdate Pocket Vapor target with a 50x30 monochrome grid, 1bpp font lowering, CLI/build integration, and browser preview
• add an official Playdate C SDK runtime with direct framebuffer rendering, dirty-row commits, D-pad input, and short/long A/B mappings for the Todo demo
• add SDK discovery, safe Make project generation, .pdx packaging, build/open scripts, tests, and target documentation

Validation

• bun test vapor/tests/ — 57 pass, 0 fail, 7337 assertions
• bunx tsc --noEmit -p vapor
• bun run vapor:check
• bun run vapor:playdate — clean SDK 3.1.1 build, 42.2 KB .pdx
• bun run vapor:playdate:play — cold-launched in the official Simulator
• manually exercised D-pad, filter, short A/B, hold-A new/save, and hold-B clear/cancel in the official Simulator
• verified custom SDK paths and output names containing spaces, $, and ;

Scope

This builds and validates the host pdex.dylib bundle for the official Playdate Simulator. It does not claim an ARM device build or physical Playdate validation.