feat(rockbox): add iPod classic PocketJS host

[gfhdhytghd]

Summary

• add a development-only Rockbox ipod6g host for the 320x240 iPod classic
• embed the PocketJS guest, QuickJS, and software rasterizer in a .rock plugin
• map click-wheel and hardware buttons to the portable PocketJS input contract
• add build/bootstrap tooling, compatibility shims, documentation, and host/profile tests

Validation

• bun rockbox bootstrap (fresh apply and idempotent re-run)
• bun rockbox test
• bunx tsc --noEmit
• 40 shared/runtime and Rockbox profile tests passed
• clean hardware build against Rockbox 420537c864 produced pocketjs-ipod6g.rock (1,082,768 bytes)
• deployed byte-identically to .rockbox/rocks/apps/pocketjs.rock on an ipod6g after updating it to the matching official daily build

Physical launch and click-wheel acceptance remain pending.