docs: restructure documentation with quickstart, concepts, and new nav #520

Job	Run time
checks / readme-snippets	12s
checks / pre-commit	37s
checks / test (3.10, locked, windows-latest)	2m 12s
checks / test (3.11, lowest-direct, ubuntu-latest)	44s
checks / test (3.10, lowest-direct, ubuntu-latest)	49s
checks / test (3.11, lowest-direct, windows-latest)	2m 29s
checks / test (3.10, lowest-direct, windows-latest)	2m 19s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 4s
checks / test (3.10, locked, ubuntu-latest)	47s
checks / test (3.14, lowest-direct, windows-latest)	2m 20s
checks / test (3.13, lowest-direct, ubuntu-latest)	46s
checks / test (3.12, locked, ubuntu-latest)	48s
checks / test (3.12, lowest-direct, ubuntu-latest)	47s
checks / test (3.14, locked, windows-latest)	2m 56s
checks / test (3.12, lowest-direct, windows-latest)	3m 27s
checks / test (3.11, locked, windows-latest)	2m 32s
checks / test (3.12, locked, windows-latest)	3m 40s
checks / test (3.13, locked, windows-latest)	3m 16s
checks / test (3.13, lowest-direct, windows-latest)	2m 29s
checks / test (3.14, locked, ubuntu-latest)	2m 14s
checks / test (3.13, locked, ubuntu-latest)	42s
checks / test (3.11, locked, ubuntu-latest)	43s
all-green	4s
	37m 57s

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