fix: use REST API for user search to fix incorrect sort order

[unhappychoice]

Fixes #112

Summary

The GraphQL user search uses sort:followers-desc in the query string, but GitHub does not support the sort:followers qualifier for user search. This causes non-deterministic results and missing users in the rankings.

Changes

Replaces the single GraphQL search query with a two-step approach:

1. REST API GET /search/users?sort=followers&order=desc for collecting user logins — the REST API officially supports sort=followers and returns correctly sorted results with no duplicates
2. GraphQL user(login:) batch queries (10 users/batch) for fetching detailed data (contributions, organizations, follower counts)

Other changes

• MinFollowers field added to UserSearchQuery and QueryPreset — the worldwide preset uses minFollowers: 1000 to narrow the search scope. Without this filter, the REST API search may hit GitHub's time limit and return partial results (the response's incomplete_results field would be true), since worldwide has 160M+ users.
• minFollowers() fix — computes the actual minimum across all users instead of using the last user's follower count
• Exclude claude account — the Anthropic Claude Code co-author account causes GitHub GraphQL to return 504 on contributionsCollection due to its massive co-authored commit volume
• Exponential backoff retry for GraphQL batch errors
• Rate limit delays (2s) between REST pages and GraphQL batches to avoid secondary rate limits

Testing

Verified with production settings (consider=1000, amount=256):

• Japan preset: 1000 users fetched, 0 duplicates, all REST API pages returned complete results, top user keijiro (23,372 followers) → bottom user ucan-lab (214 followers)
• Worldwide preset: 999 users fetched (claude excluded), 0 duplicates, all REST API pages returned complete results, top user torvalds (283,302 followers) → bottom user Aakashdeveloper (4,489 followers)

Files changed

File	Change
github/github.go	Rewrite SearchUsers() to use REST + GraphQL two-step approach
presets.go	Add minFollowers field to QueryPreset; set minFollowers: 1000 for worldwide
top/top.go	Add MinFollowers to Options struct; pass through to UserSearchQuery
main.go	Read preset.minFollowers and pass to top.Options

[unhappychoice]

BTW, thank you for maintaining this project! I really appreciate the work you've put into it.

[ashkulz]

@unhappychoice thank you for the fanastic analysis! I'm a bit tied up right now, I'll review this on Wednesday.

I'm standing on the shouders of giants -- @lauripiispanen did most of the work, and I'm just keeping the lights running 🙂