feat: use GitHub star history API for trends

[pastelsky]

Summary

• add the trends data-source and cache-service foundation on the current bundlephobia branch
• use GitHub's official privacy-safe /stargazers/history endpoint for exact daily star actions
• keep current stargazers_count as a separate live snapshot
• remove issue history and current issue counts from the trends contract for now
• remove the ClickHouse and OSS Insight GitHub-history fallbacks so the source contract is explicit
• paginate only as far back as the requested range, validate weekly totals, and expose source/completeness metadata

Data contract

The historical stars series is star actions, not cumulative star stock. Issue history and issue snapshots are intentionally absent from this feature until a reliable historical source is available.

This supersedes the older cache protocol in #1089; do not merge both implementations. It is the backend/data-source PR to review before wiring the page in #1076.

Validation

• yarn format:check
• yarn typecheck
• yarn lint (existing warnings only)
• focused trends tests: 11 passed
• yarn build
• full Jest: 136 passed; 5 existing errors-cache fixture failures remain in the local environment

The GitHub endpoint documentation is at https://docs.github.com/en/rest/activity/starring?apiVersion=2026-03-10.

[pastelsky]

I thought we had an npm dep for this?