feat(workshop): add canonical min/max variable modifiers

[Teakowa]

Summary

• add canonical ModifyOp::Min and ModifyOp::Max identities and catalog linkage
• parse and emit global, player, and indexed variable modification forms, including min= and max=
• reject unsupported named assignment operators explicitly
• add parser, WIR, catalog, locale round-trip, and oracle-contract coverage

Verification

• cargo fmt --all -- --check
• cargo run --locked -p workshop-rs --bin workshop-catalog-gen -- check
• cargo test --locked --workspace --all-targets --no-fail-fast
• cargo clippy --locked --workspace --all-targets -- -D warnings

OverPy and Workshop.codes define Max/Min as variable modification operations. Live-client execution is outside this PR.

Fixes #95