feat(cli): add --ref benchmark reference context output

[anirudw]

1. Adds --ref CLI flag to include pinned benchmark reference context in text reports
2. Adds reference baseline generator and committed baseline
3. Extends reporter options API for optional reference output
4. Adds tests for parsing, validation, rendering, and baseline consistency
5. Keeps --ref incompatible with --json and --lint by design

[benvinegar]

Thanks for submitting! Will take a look.