Lower OPY assignment and expression primitives into canonical Workshop WIR

[Teakowa]

Parent: #41
Depends on: #40 (completed)

Goal

Complete the non-control-flow statement/value lowering that can map directly or by evidence-backed normalization into the existing canonical workshop-rs WIR surface.

Scope

• Complete global/player assignment and modification lowering, including source-attributed target spans.
• Lower the WIR-representable expression surface required by conditions/actions: literals, arrays, vectors, global/player/event-player references, indexing, formatting, and binary/unary operations.
• Handle frontend-resolved constants and macro-expanded semantic forms where they remain in HIR without re-parsing source or reproducing upstream compiler internals.
• Treat pass and other source-level no-op forms according to pinned observable semantics rather than silently dropping unknown nodes.
• Preserve source provenance and stable structured diagnostics for forms that cannot yet lower.
• Keep receiver/member/catalog-dependent semantics assigned to Close catalog-backed OPY lowering and corpus evidence #42.
• Add minimized oracle-backed positive/negative integration fixtures and validate emitted WIR structurally.

Non-goals

• if/loops/doWhile/switch/break control-flow lowering (Lower OPY control flow into canonical Workshop WIR with oracle evidence #47).
• Closing receiver/member/enum/catalog breadth (Close catalog-backed OPY lowering and corpus evidence #42).
• Settings, locale, optimizer directives, post-compile hooks, or decompilation.
• Introducing a temporary IR or copying Workshop data.

Acceptance criteria

• In-scope assignment/modification and expression forms either lower to valid canonical WIR or fail with stable source-attributed diagnostics.
• Player/global variable semantics retain canonical WIR identity and provenance.
• No unsupported HIR node is silently discarded or guessed.
• Oracle-backed fixtures cover representative expression/assignment behavior and negative paths.
• Program::validate and workspace CI are green.
• Lower OPY control flow into canonical Workshop WIR with oracle evidence #47 can build control-flow lowering on the resulting value/action primitives without redesigning the boundary.