[alpha.7] Auto-sync OPENELEMENT_EXPORT_FILES from package export maps

[SisyphusZheng]

packages/adapter-vite/src/ssg-package-resolver.ts duplicates every package export map in OPENELEMENT_EXPORT_FILES. This is currently kept in sync manually and is a maintenance hazard.

Acceptance:

• Add a script or build step that generates OPENELEMENT_EXPORT_FILES from each packages/*/deno.json exports.
• Run the sync in CI and fail if the generated output does not match the committed file.
• Remove the manual mapping or keep it as a generated artifact.

Context: packages/adapter-vite/src/ssg-package-resolver.ts, tools/check-package-surface.ts.

[SisyphusZheng]

Resolved by PR #370 (auto-sync OPENELEMENT_EXPORT_FILES). Merged to dev.