d2dagre: use native Go Dagro port

[alixander]

Summary

• replace the embedded Dagre JavaScript bundle and Goja execution with the native Go Dagro module
• preserve D2's existing graph construction, label sizing, parent ordering, multiedge naming, and route post-processing
• remove the JavaScript assets, embedding code, and release-build workaround
• update layout documentation, plugin help, attribution, and the release changelog
• ship the Dagro/Dagre/Graphlib MIT notice in native, MSI, and npm/WASM artifacts, and include D2's MPL in the npm package

Why

D2's default Dagre layout currently embeds Dagre 0.8.5 as JavaScript and creates a JavaScript VM for every layout. Dagro is a behavior-compatible Go port of that exact implementation, allowing D2 to use a native Go layout path without changing diagram output.

Impact

Existing Dagre layout behavior is preserved. All 313 stored Dagre board JSON and SVG fixtures pass exactly; no goldens were updated.

Screenshots are not applicable because the expected and produced SVGs are byte-for-byte unchanged.

Dependency

Uses Dagro v0.1.0, released from merged PR d2lang/dagro#1.

Validation

• go test ./d2layouts/d2dagrelayout -count=1
• go vet ./d2layouts/d2dagrelayout
• GOOS=js GOARCH=wasm go build -o /dev/null ./d2js
• go test ./e2etests -run '^TestE2E$' -count=1 with board and SVG checks enabled
• host macOS and cross-compiled Windows release archives contain the byte-identical third-party notice
• npm pack --dry-run --json includes both LICENSE.txt and THIRD_PARTY_NOTICES.txt; publish staging also verifies their packed bytes
• release shell syntax and the WiX source validate locally
• Dagro differential, race, and vet suites in Port Dagre 0.8.5 to Go dagro#1