feat(symbian): add native Pocket3D extensions

[doodlewind]

Summary

• add a versioned app-specific Symbian native extension ABI with safe PAK ownership and GL context-loss teardown
• add a no_std Pocket3D GLES2 backend for BSP worlds, progressive textures, actors, effects, and viewmodels
• allow locked single-app custom cores in the reproducible E7 packager without affecting the production target registry

Validation

• bun x tsc --noEmit
• full bun run test
• Symbian/npm targeted tests: 16/16
• PocketJS core 100/100, UI surface 5/5, Symbian core 10/10
• Pocket3D GLES2/Vita/BSP 39/39
• web pixel golden 49/49 and tape hashes 180/180
• exact armv6 Symbian cross-build
• real pinned GCCE -> elf2e32 -> signed SIS build (sha256 e32f57cb8ee315ab4bfeb72355868ef026d31e21ea80b46af85e28c118c28339)

Review

Independent P0-P2 review found and closed writable PAK aliasing, context-loss teardown, and custom-core/catalog ambiguity; re-review is clean.