feat(lowering): add core HIR to Workshop WIR path

[Teakowa]

Summary

Stacked on del-rs#29, this PR advances del-rs#30 and the parent del-rs#8.

• Consumes released workshop-rs 0.1.1, including the completed canonical rule-event contract from workshop-rs#12.
• Preserves provider-produced canonical bindings in backend-neutral HIR.
• Adds the DEL-owned HIR -> workshop_rs::wir::Program lowering API with source-file/span provenance.
• Lowers deterministic global/player variables, explicit source IDs, reservations, top-level initializers, core rule events, conditions, literals, arrays, canonical enum constants, external action/value calls, assignments/modifications, if/while/auto-for, and subroutine tables/calls.
• Validates structural WIR and canonical Workshop identities; unsupported forms return HI018 and do not emit an incomplete rule.

This is intentionally a partial #30 implementation. Object/reference runtime encodings, local Workshop storage strategy, classic for/foreach/switch, named-action argument reordering, and other advanced lowering remain explicit follow-up work.

Validation

• cargo build --all-targets
• cargo test --all-targets
• cargo test --test matrix
• cargo test --test corpus
• focused cargo test --test workshop_lowering --test workshop_provider
• rustfmt --edition 2021 --check src/workshop.rs tests/workshop_lowering.rs
• git diff --check

Existing warnings remain unchanged in the frontend; no warning policy was weakened.