docs: restructure documentation with quickstart, concepts, and new nav #521

Job	Run time
checks / pre-commit	37s
checks / readme-snippets	11s
checks / test (3.10, locked, windows-latest)	2m 10s
checks / test (3.10, lowest-direct, ubuntu-latest)	44s
checks / test (3.11, lowest-direct, ubuntu-latest)	48s
checks / test (3.10, lowest-direct, windows-latest)	2m 36s
checks / test (3.11, lowest-direct, windows-latest)	2m 30s
checks / test (3.12, lowest-direct, windows-latest)	3m 25s
checks / test (3.11, locked, windows-latest)	2m 16s
checks / test (3.13, lowest-direct, windows-latest)	2m 37s
checks / test (3.11, locked, ubuntu-latest)	45s
checks / test (3.13, lowest-direct, ubuntu-latest)	44s
checks / test (3.12, locked, windows-latest)	3m 49s
checks / test (3.13, locked, ubuntu-latest)	44s
checks / test (3.10, locked, ubuntu-latest)	49s
checks / test (3.12, locked, ubuntu-latest)	52s
checks / test (3.14, locked, windows-latest)	3m 19s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 13s
checks / test (3.13, locked, windows-latest)	3m 22s
checks / test (3.12, lowest-direct, ubuntu-latest)	50s
checks / test (3.14, lowest-direct, windows-latest)	2m 17s
checks / test (3.14, locked, ubuntu-latest)	2m 13s
all-green	3s
	38m 54s

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