docs: restructure documentation with quickstart, concepts, and new nav #518

Job	Run time
checks / readme-snippets	10s
checks / pre-commit	29s
checks / test (3.12, locked, windows-latest)	3m 31s
checks / test (3.11, lowest-direct, ubuntu-latest)	53s
checks / test (3.13, lowest-direct, ubuntu-latest)	54s
checks / test (3.13, lowest-direct, windows-latest)	2m 53s
checks / test (3.10, lowest-direct, windows-latest)	2m 30s
checks / test (3.11, locked, ubuntu-latest)	51s
checks / test (3.10, lowest-direct, ubuntu-latest)	55s
checks / test (3.11, locked, windows-latest)	2m 49s
checks / test (3.10, locked, ubuntu-latest)	48s
checks / test (3.12, lowest-direct, windows-latest)	3m 52s
checks / test (3.12, locked, ubuntu-latest)	55s
checks / test (3.12, lowest-direct, ubuntu-latest)	57s
checks / test (3.10, locked, windows-latest)	2m 19s
checks / test (3.14, locked, ubuntu-latest)	2m 16s
checks / test (3.13, locked, windows-latest)	2m 37s
checks / test (3.14, lowest-direct, windows-latest)	2m 21s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 23s
checks / test (3.14, locked, windows-latest)	3m 10s
checks / test (3.11, lowest-direct, windows-latest)	2m 33s
checks / test (3.13, locked, ubuntu-latest)	47s
all-green	4s
	39m 57s

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