feat(runtime): preserve init exit status through wait

[ZhiXiao-Lin]

Summary

• add protocol-v2 guest wait with protocol-v1 compatibility
• preserve exact normal exit codes or terminating signals across repeated waits
• expose wait only for drivers that advertise it and validate driver inventories
• prove bounded and nonblocking waits in native Linux and utility-VM lifecycle gates
• update versioned evidence, CI assertions, roadmap, and platform documentation

Validation

• cargo fmt --all -- --check
• cargo test --workspace --all-targets
• cargo clippy --workspace --all-targets -- -D warnings
• RUSTDOCFLAGS="-D warnings" cargo doc --workspace --no-deps
• Clippy cross-checks: aarch64/x86_64 Linux and x86_64 Windows
• ShellCheck, bash syntax, and actionlint
• real Apple Silicon HVF: agent-vm, OCI lifecycle, multi-container lifecycle, and all three no-delete cleanup phases

Stack

This PR is based on feat/pidfd-signaling and should be reviewed after that branch.