docs: update build performance benchmarks

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Automated build benchmark update from workflow run #59.

[greptile-apps]

Greptile Summary

Automated benchmark update reflecting improved native build performance (2.1 ms/file, down from 2.2) and updated graph metrics for v2.4.0.

• Native build speed improved ~5% (2.2 → 2.1 ms/file)
• 50k files estimate reduced from 110s to 105s
• Graph size increased: 644 nodes (+4), 1,062 edges (+13)
• Query time regressed slightly (1.6 → 1.8 ms)
• All metrics internally consistent across both files

Confidence Score: 5/5

• This PR is safe to merge with no risk
• Automated documentation-only update from CI workflow with internally consistent numeric changes across both files
• No files require special attention

Important Files Changed

Filename	Overview
README.md	Updated native build speed from 2.2 to 2.1 ms/file and 50k files estimate from 110s to 105s
generated/BUILD-BENCHMARKS.md	Updated v2.4.0 benchmark metrics including build times, nodes, edges, and DB size with recalculated percentage deltas

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