feat: validate module bodies and export constants

[Lord1Egypt]

Summary

• check imported module bodies in isolated scopes without executing them
• wrap imported checker failures as stable E0033 diagnostics
• infer and export typed top-level module constants
• evaluate pure module constants once and expose them at runtime
• add corpus coverage for constant imports on both engines

Verification

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

[gemini-code-assist]

Caution

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