docs: update build performance benchmarks (2.6.0)

[github-actions]

Automated build benchmark update for 2.6.0 from workflow run #128.

[greptile-apps]

Greptile Summary

Automated benchmark update for version 2.6.0 with verified calculations and consistent formatting.

Key Changes:

• Updated performance metrics in README.md for v2.6.0 (146 files, up from 126)
• Added comprehensive benchmark data to BUILD-BENCHMARKS.md including build times, query performance, and incremental rebuild metrics
• All per-file calculations verified: 293ms / 146 files = 2 ms/file (native), 1149ms / 146 files = 7.9 ms/file (WASM)
• Trend indicators (↑↓~) correctly show percentage changes from v2.5.1
• JSON benchmark data structure matches previous versions

Performance observations from the data:

• Some regressions in build and query times (expected as codebase grew from 126 to 146 files)
• Query: fn-deps improved from 1.8ms to 1.3ms (28% faster)

Confidence Score: 5/5

• This PR is safe to merge with minimal risk - automated documentation update with verified data integrity
• Score reflects that this is an automated, documentation-only PR with all benchmark calculations verified as mathematically correct, consistent formatting matching previous versions, and no code changes
• No files require special attention - both are generated documentation with verified data

Important Files Changed

Filename	Overview
README.md	Updated performance metrics table with version 2.6.0 benchmarks - all values correctly calculated
generated/benchmarks/BUILD-BENCHMARKS.md	Added comprehensive 2.6.0 benchmark data across all tables with correct calculations and trend indicators

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