Route undefined binding diagnostics through WASM

[yenda]

Summary

• expose Rust semantic analysis from the WASM package via analyze(source)
• route editor allium.rule.undefinedBinding findings through the Rust/WASM analyzer instead of the duplicated TypeScript text parser
• remove the TypeScript rule-binding collector and map Rust byte spans to editor positions
• move the remaining TS-only undefined-binding cases (exists candidate, for item in items) into the Rust analyzer
• document in docs/project/rust-checker-parity.md that allium.rule.undefinedBinding is now a migrated Rust/WASM-owned diagnostic for editor/LSP surfaces

Rationale

The existing project docs describe the TypeScript/Rust analyzer split as a transitional state: TypeScript served the editor/LSP first, while Rust/WASM was introduced later as the parser-backed path. Keeping semantic diagnostics duplicated creates drift risk; this PR migrates one concrete diagnostic lane to the Rust implementation without broadening the scope to unrelated checks.

Stack

This is logically stacked on #36 (Fix typed trigger parameter bindings) to keep the original bug fix separate from the analyzer ownership change.

Because this branch comes from a fork and the stack base branch is not available in the upstream repository, this PR targets main. Until #36 merges, GitHub's aggregate diff includes the #36 commit; the intended review scope here is the two follow-up commits after Fix typed trigger parameter bindings.

After #36 merges, this PR can be rebased or retargeted so its diff contains only the WASM migration commits.

Verification

• cargo test --workspace
• cargo fmt -p allium-wasm --check
• wasm-pack build crates/allium-wasm --target nodejs --out-dir ../../packages/allium-parser-wasm
• npm run lint (exits 0; reports existing warnings in generated ignored WASM .d.ts files)
• npm run test
• git diff --check