Add bound test sessions, richer selectors, and Maestro YAML support

[DjDeveloperr]

Summary

• Bind simdeck/test sessions to a default UDID via connect({ udid }) and keep legacy per-call UDID overrides working.
• Expand selector and assertion support with richer matching, negative assertions, and scrollUntilVisible across the JS API and REST surface.
• Add a Rust CLI simdeck maestro test runner for common Maestro YAML flows, with artifact output for failures and screenshots.
• Update docs and operator guidance to describe the new testing model and compatibility scope.

Testing

• cargo test --manifest-path server/Cargo.toml passed.
• cargo fmt --manifest-path server/Cargo.toml passed.
• npm run --prefix packages/simdeck-test build passed.
• git diff --check passed.