feat: type capabilities and standard namespaces

[Lord1Egypt]

Summary

• replace the checker Sys placeholder with structural capability namespace types
• register exact signatures for all eight frozen std modules
• type concrete str/list/map methods and variadic sys.print
• reject invalid member names, arity, and argument types during checking

Verification

• cargo test --release
• cargo clippy --all-targets -- -D warnings
• cargo fmt --check
• tools/phase0_audit.py check

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.