docs: cleanup README and AGENTS.md

[not-matthias]

• fix(readme): update repo URLs, Discord link, and project structure
• fix(agents): remove stale Justfile profiling section

[codspeed-hq]

Merging this PR will degrade performance by 18.99%

⚡ 1 improved benchmark
❌ 1 regressed benchmark
✅ 123 untouched benchmarks
⏩ 9 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	dualPivotQuickSort[100]	14.2 µs	11.2 µs	+27.32%
❌	timSort[100]	8.7 µs	10.7 µs	-18.99%

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_{Comparing fix/readme-and-agents-cleanup (76a2b88) with main (8cb09f5)}

Footnotes

1. 9 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩