fix: sort snapshot list output

[saurabhhhcodes]

Summary

• sort snapshot tags alphabetically in listSnapshots() before rendering apidrift list output
• add Jest coverage that ignores non-JSON files and verifies sorted tag order

Fixes #6

Validation

• git diff --check
• node --check src/storage/snapshotStore.js
• node --check tests/storage/snapshotStore.test.js
• npm test -- --runInBand could not run locally because npm is not available in this shell

GSSoC labels requested

Please add/keep gssoc and any required difficulty/type scoring labels if this is accepted.

[saurabhhhcodes]

Hi maintainer, this is still a clean small-scope fix and remains mergeable. The branch only tightens snapshot list ordering and adds focused storage tests, so it should stay low-risk to review. If the scope still looks good on your side, please also copy the appropriate GSSoC labels onto the PR when reviewing.