docs: restructure documentation with quickstart, concepts, and new nav #519

Job	Run time
checks / pre-commit	35s
checks / readme-snippets	14s
checks / test (3.10, locked, windows-latest)	2m 20s
checks / test (3.11, locked, windows-latest)	3m 20s
checks / test (3.10, lowest-direct, windows-latest)	2m 48s
checks / test (3.11, locked, ubuntu-latest)	47s
checks / test (3.11, lowest-direct, ubuntu-latest)	53s
checks / test (3.10, lowest-direct, ubuntu-latest)	52s
checks / test (3.11, lowest-direct, windows-latest)	2m 35s
checks / test (3.10, locked, ubuntu-latest)	50s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 20s
checks / test (3.12, lowest-direct, windows-latest)	3m 32s
checks / test (3.12, locked, windows-latest)	3m 34s
checks / test (3.14, locked, windows-latest)	3m 45s
checks / test (3.13, lowest-direct, windows-latest)	2m 37s
checks / test (3.14, locked, ubuntu-latest)	2m 24s
checks / test (3.14, lowest-direct, windows-latest)	2m 49s
checks / test (3.13, locked, ubuntu-latest)	47s
checks / test (3.13, locked, windows-latest)	2m 28s
checks / test (3.13, lowest-direct, ubuntu-latest)	51s
checks / test (3.12, locked, ubuntu-latest)	55s
checks / test (3.12, lowest-direct, ubuntu-latest)	55s
all-green	4s
	41m 15s

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