feat: add review timing overview

[vahapogut]

Fixes #284

@algora-pbc /claim #284

Summary

• Add first-review timing metadata while fetching PR reviews.
• Carry reviewed PR timing entries into the weekly overview generation pipeline.
• Render a Review Timing table for every PR that received a review, sorted by slowest time to first review.

Verification

• bun test
• bun x tsc --noEmit
• bun run format:check
• bun run build
• git diff --check

[vercel]

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