Add Zstandard to native PHP runtimes

[chubes4]

Summary

• build the Zstandard PHP extension into macOS and Linux native runtimes
• package and enable the PECL Zstandard extension on Windows
• verify Windows runtime assembly loads Zstandard

This is the runtime prerequisite for portable .fig imports. It keeps decompression inside Studio’s packaged PHP runtime rather than relying on a host-installed zstd executable.

Testing

• npm test -- apps/cli/lib/native-php/tests/config.test.ts
• npm exec eslint -- apps/cli/lib/native-php/config.ts apps/cli/lib/native-php/tests/config.test.ts
• npm exec tsc -- --noEmit --pretty false -p apps/cli/tsconfig.json
• git diff --check
• cross-platform PHP workflow build to follow on this branch

AI assistance

OpenAI GPT-5.6 Sol via OpenCode inspected the native runtime packaging paths, implemented the cross-platform extension wiring, and ran the focused verification commands. The implementation and resulting diff were reviewed by Chris Huber.