fix(changelog): Default workspace changelog to its directory

[BYK]

Summary

• Default an unconfigured changelog path to <workspace>/CHANGELOG.md when the selected workspace is a real directory; keep explicit paths and root defaults for aliases and single-package repositories.
• Use the same normalized path for release preparation and GitHub publication. Reject workspace directories that resolve outside the repository.
• Document the default and test config resolution, GitHub target selection, and an isolated dry-run release with a distinct root changelog.

Validation

• The directory-workspace regression failed against the old root default, passed with the fix, and failed again when the guard was removed.
• pnpm run build, pnpm run typecheck, pnpm run lint, pnpm exec vitest run --printConsoleTrace (1,236 passed, 1 skipped), and pnpm run format:check passed. ESLint emitted seven pre-existing unused-binding warnings.

This lets getsentry/toolkit#1362 omit the explicit packages/cli/CHANGELOG.md override as requested.

[github-actions]

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2026-10-02 14:07 UTC

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