docs: restructure documentation with quickstart, concepts, and new nav #527

Job	Run time
checks / readme-snippets	13s
checks / pre-commit	30s
checks / test (3.11, lowest-direct, windows-latest)	3m 2s
checks / test (3.11, lowest-direct, ubuntu-latest)	47s
checks / test (3.12, lowest-direct, windows-latest)	4m 39s
checks / test (3.10, locked, ubuntu-latest)	48s
checks / test (3.11, locked, windows-latest)	2m 29s
checks / test (3.10, lowest-direct, windows-latest)	3m 6s
checks / test (3.11, locked, ubuntu-latest)	50s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 0s
checks / test (3.12, locked, windows-latest)	3m 59s
checks / test (3.12, locked, ubuntu-latest)	58s
checks / test (3.10, lowest-direct, ubuntu-latest)	53s
checks / test (3.10, locked, windows-latest)	2m 40s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 18s
checks / test (3.13, lowest-direct, windows-latest)	2m 54s
checks / test (3.13, locked, ubuntu-latest)	47s
checks / test (3.13, locked, windows-latest)	2m 40s
checks / test (3.14, lowest-direct, windows-latest)	2m 31s
checks / test (3.13, lowest-direct, ubuntu-latest)	48s
checks / test (3.14, locked, ubuntu-latest)	2m 22s
checks / test (3.14, locked, windows-latest)	3m 10s
all-green	3s
	42m 27s

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