refactor(core): share canonical JSON serializer with eval and storage

[seekskyworld]

Problem

The headless package now has one canonical JSON implementation, but packages/eval/src/experiment-directory.ts and packages/storage/src/session-bundle-manifest.ts still carry separate serializers. They encode the same sorted-object/JSON primitive rules independently, so changes to canonicalization can silently produce different experiment identities and bundle bytes.

Scope

• Expose the existing strict canonical JSON authority from @maka/core through a neutral module name.
• Replace the eval and session-bundle copies with that authority.
• Preserve the manifest's stable SessionBundleFileError for invalid values and the eval newline/file format.
• Leave runtime-host serializers for a separately coordinated change because their undefined policies are distinct and their files are under active PRs.

Acceptance criteria

• Equivalent key order produces identical bytes in both consumers.
• Manifest encoding still rejects non-finite/unsupported values with its existing public error code.
• Experiment directory creation and collision checks retain their current output and newline behavior.
• Focused core, eval, and storage tests cover deterministic ordering, nested arrays/objects, and invalid values.

This is a child slice of the canonicalization audit in #1404.

[seekskyworld]

我认领这个 canonical JSON 切片。会把现有严格 serializer 暴露为中性 core authority，迁移 eval 与 session-bundle manifest，显式保留 manifest 错误码和 eval 换行格式，并补齐跨包行为测试；runtime-host 的 undefined 语义留给后续协调。