docs: replace MkDocs with Zensical #3434

Job	Run time
checks / docs	44s
checks / readme-snippets	14s
checks / pre-commit	1m 7s
checks / test (3.12, locked, windows-latest)	2m 7s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 26s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 19s
checks / test (3.13, locked, ubuntu-latest)	1m 16s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 26s
checks / test (3.11, locked, windows-latest)	2m 9s
checks / test (3.11, lowest-direct, windows-latest)	2m 5s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 21s
checks / test (3.11, locked, ubuntu-latest)	1m 22s
checks / test (3.12, locked, ubuntu-latest)	1m 39s
checks / test (3.10, lowest-direct, windows-latest)	1m 50s
checks / test (3.10, locked, ubuntu-latest)	1m 28s
checks / test (3.10, locked, windows-latest)	2m 5s
checks / test (3.13, locked, windows-latest)	2m 8s
checks / test (3.13, lowest-direct, windows-latest)	2m 3s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 32s
checks / test (3.12, lowest-direct, windows-latest)	1m 51s
checks / test (3.14, lowest-direct, windows-latest)	2m 21s
checks / test (3.14, locked, windows-latest)	1m 59s
checks / test (3.14, locked, ubuntu-latest)	1m 23s
all-green	3s
	36m 58s

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