fix: expose documented package subpaths

[rogerchappel]

Summary

• export the documented @bargekit/core/fixture-io and @bargekit/core/recorder entry points
• derive the consumer import matrix directly from docs/API.md
• pack and install the package in a fresh temporary consumer, then verify every documented import and its packed implementation target

Verification

• Tests or checks run: npm ci; npm run release:check; git diff --check
• Manual review completed: confirmed the packed tarball includes src/fixture-io.js and src/recorder.js; confirmed open PRs ci: bump actions/checkout from 4 to 7 #9 and ci: bump actions/setup-node from 4 to 7 #15 only update Actions

Risk Level

• Low
• Medium
• High

Notes:

• Commit addb83b exposes the two existing modules through the package export map.
• Commit b249a55 adds the packed-consumer regression and wires it into package:smoke, which is already part of release:check.
• The full release check passed all 35 tests and successfully imported all seven package specifiers documented in docs/API.md.

Rollback Plan

• Revert the two commits to restore the prior export map and package smoke behavior.

Human Decision Needed

• None
• Maintainer review
• Product/design decision
• Security/privacy review
• Other: