test(migration): make workdir bucket hash expectation platform-aware

[haosenwang1018]

Related Issue

Part of #225

Problem

computeWorkdirBucket() intentionally hashes resolve(workdirPath), matching the running app's workdir key behavior. One test hardcoded the expected hash from the raw POSIX-looking string '/Users/me/Developer/proj'. That is stable on POSIX, but on Windows resolve() re-anchors the input to the current drive, so the product function and the test expected value diverge even though the function is behaving as documented.

What changed

• Updated the test expected hash to derive from resolve(input), the same normalization contract used by computeWorkdirBucket().
• Kept the existing slug and hash-shape assertions intact.
• Added an empty changeset because this is a test-only portability fix with no published package bump.

Verification

• pnpm --filter @moonshot-ai/migration-legacy exec vitest run test/sessions/workdir-bucket.test.ts
• pnpm --filter @moonshot-ai/migration-legacy run typecheck
• pnpm exec oxlint packages/migration-legacy/test/sessions/workdir-bucket.test.ts
• pnpm --filter @moonshot-ai/migration-legacy run test
• pnpm changeset status --since=origin/main

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

🦋 Changeset detected

Latest commit: a1b491c

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