fix: improve contributor fallback and author visibility

[beanbean9339]

Summary

This PR improves GitHub contributor fallback and author discovery when importing repository metadata.

Changes

• Filter automated GitHub accounts from contributor fallback authors.
• Retain eligible anonymous human contributors returned by GitHub.
• Discover human authors from repository commit history when contributor metadata is incomplete.
• Add authenticated pagination for deeper commit-history scans.
• Add unauthenticated safety limits to avoid excessive GitHub API requests.
• Filter GitHub username-like values from citation authors.
• Normalize and deduplicate discovered authors.
• Keep imported authors visible in the metadata form.
• Add regression tests for fallback limits, anonymous authors, bot filtering, commit history, and hyphenated names.
• Document fallback and rate-limit behavior.

Validation

• npm test
• 122 tests passing

[beanbean9339]

Closing as a duplicate of the original broad change set. The focused work is now in #64 (issue #56), #67 (author-list UI), #70 (anonymous/hyphenated names), and #71 (commit-history authors), all targeting main. The previous full content remains preserved in backup/pr64-all-work for reference while the split PRs are reviewed.