WASM `check()` silently accepts unsupported `sourceMap` option — add `parse_check_options` validation to match napi surface

[dean0x]

Background

crates/mds-wasm/src/lib.rs:429 exposes a check() binding that accepts a JS options object but has no parse_check_options allow-list. This means passing sourceMap: true to WASM check() is silently ignored — the option is accepted without error and has no effect.

Ledger ID: #41 (consistency-mds-wasm/src/lib.rs:429-check_accepts_sourcemap)
File: crates/mds-wasm/src/lib.rs:429, 719-741
Originating reviewer: Consistency

Problem

• mds-napi's check binding already has a dedicated parse_check_options that rejects unknown keys via assertKnownKeys.
• The universal package (@mdscript/mds) routes through assertKnownKeys and shields browser/Node consumers.
• Direct WASM consumers (@mdscript/mds-wasm) have no such protection: unknown keys are accepted and discarded.
• PR fix: v0.4.0 remediation — dogfooding blockers, bug batch, UX polish, docs sweep #196 added documentation of the correct WASM option set (fixing chore(ci): bump dtolnay/rust-toolchain from 1.88 to 1.100 #40), but did not add enforcement — the documentation now accurately describes what the correct behavior should be, making the enforcement gap more visible.

Why deferred from PR #196

Adding a parse_check_options allow-list on the WASM check binding introduces a new rejection path that would break direct WASM consumers currently passing sourceMap (expecting it to work or unaware it is unsupported). This is a behavior change on a binding surface that should not land immediately before a publish. The documentation half (#40) was the correct in-scope fix for this PR.

Proposed change

Add parse_check_options(opts: JsValue) -> CheckOptions in mds-wasm/src/lib.rs modeled on parse_lint_options, with an allow-list matching the documented set from packages/mds-wasm/README.md. Throw TypeError on unknown keys. Wire it into check().

Acceptance Criteria

• parse_check_options implemented in mds-wasm/src/lib.rs with allow-list matching the documented option surface
• Passing sourceMap: true to WASM check() throws a TypeError with a clear message
• WASM check tests cover the rejection path
• CHANGELOG [Unreleased] notes this as a breaking change for direct WASM consumers (if applicable)
• @mdscript/mds universal package behavior unchanged (it already routes through napi's assertKnownKeys)

Deferred from: PR #196

[dean0x]

Closing as implemented.

parse_check_options was added at crates/mds-wasm/src/lib.rs:548-575 and wired into the check() public API at line 770. It validates the options object with an allow-list covering filename, modules, and vars, matching the napi surface exactly. No caller-visible option is silently accepted and ignored.