docs: modernize development guidelines and rename to AGENTS.md #1813

Job	Run time
checks / pre-commit	38s
checks / readme-snippets	12s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 2s
checks / test (3.10, locked, windows-latest)	2m 18s
checks / test (3.10, locked, ubuntu-latest)	56s
checks / test (3.10, lowest-direct, ubuntu-latest)	55s
checks / test (3.11, lowest-direct, windows-latest)	2m 36s
checks / test (3.12, lowest-direct, windows-latest)	3m 56s
checks / test (3.14, locked, ubuntu-latest)	2m 26s
checks / test (3.13, locked, windows-latest)	2m 33s
checks / test (3.12, locked, windows-latest)	3m 13s
checks / test (3.12, locked, ubuntu-latest)	57s
checks / test (3.14, lowest-direct, windows-latest)	2m 22s
checks / test (3.13, lowest-direct, ubuntu-latest)	58s
checks / test (3.10, lowest-direct, windows-latest)	2m 57s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 21s
checks / test (3.11, locked, windows-latest)	2m 40s
checks / test (3.11, locked, ubuntu-latest)	49s
checks / test (3.14, locked, windows-latest)	4m 2s
checks / test (3.13, locked, ubuntu-latest)	50s
checks / test (3.11, lowest-direct, ubuntu-latest)	53s
checks / test (3.13, lowest-direct, windows-latest)	2m 31s
all-green	4s
	41m 9s

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