fix[notask]: emit NodeNext-compatible declaration specifiers

[localhost41]

Closes #3323.

The SDK’s post-build alias resolver was adding .js extensions to runtime imports but leaving the corresponding declaration imports extensionless. Under moduleResolution: "NodeNext", TypeScript could not follow the declaration re-export chain, so model constants appeared to be missing even though they were available at runtime.

This updates the resolver to emit .js specifiers for internal references in declaration output as well. It also handles parent-directory paths such as ../schemas, which were still present in the generated declarations.

Added a regression test that:

• checks the rewritten declaration paths;
• covers both @qvac/sdk and @qvac/sdk/models;
• runs a real tsc consumer using moduleResolution: "NodeNext";
• verifies the model constants reported in the issue;
• confirms external package subpaths are left unchanged.

Validated with:

• SDK lint
• SDK typecheck
• full SDK build
• full SDK unit suite
• Node 24 NodeNext consumer
• clean install from the generated npm tarball

Runtime JavaScript output is unchanged.

[github-actions]

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