fix(edifice-map-generator): restore deno check on the PNG codec

[BluegReeno]

Why

main has been red since 48f89fd. Committing the deployed v10 of edifice-map-generator (444fa3d) brought the pure-TS PNG codec into the repo, and its stream helpers do not type-check under Deno 2.x — 2 × TS2345 on deno check index.ts.

This is not confined to main: every open PR inherits the failure, because a PR's CI tests the merge with main. It surfaced on #72, whose own changes are unrelated.

The two type facts

Neither is cosmetic, and the fix follows from them rather than from silencing the checker:

1. CompressionStream / DecompressionStream declare writable: WritableStream<BufferSource> — wider than Uint8Array. A TransformStream<Uint8Array, Uint8Array> parameter therefore asked for something narrower than either class provides, so neither was assignable.
2. Since TypeScript 5.7, typed arrays are generic over their backing buffer: bare Uint8Array means Uint8Array<ArrayBufferLike>, which admits SharedArrayBuffer, whereas BufferSource requires ArrayBufferView<ArrayBuffer>. So a bare Uint8Array is not writable to these streams either.

The fix

Type the codec path Uint8Array<ArrayBuffer> and widen the transform parameter to TransformStream<BufferSource, Uint8Array>.

That says out loud that these buffers are never shared — which is already true: every one of them comes from new Uint8Array(n) or a Response.arrayBuffer(). A cast (as BufferSource, as any) would have silenced the checker without stating the constraint, and would have hidden the next violation of it.

Risk

Types only. The diff touches three signatures and not one executable line — TypeScript types are erased at runtime, so the deployed function is byte-for-byte unaffected in behaviour. No redeploy is implied by this PR.

Verified

With the CI's own toolchain (the denoland/deno image, same deno check index.ts the workflow runs):

• edifice-map-generator: 2 errors → clean
• hal-mcp: still clean (the other type-check step is untouched)

Unblocks

#72 (migration smoke-test), whose Migration smoke-test job already passes; only this inherited Deno type-check failure stands between it and a green CI.