docs: restructure documentation with quickstart, concepts, and new nav #528

Job	Run time
checks / readme-snippets	10s
checks / pre-commit	37s
checks / test (3.10, locked, windows-latest)	2m 17s
checks / test (3.11, lowest-direct, windows-latest)	2m 38s
checks / test (3.10, lowest-direct, windows-latest)	2m 18s
checks / test (3.11, lowest-direct, ubuntu-latest)	50s
checks / test (3.10, lowest-direct, ubuntu-latest)	50s
checks / test (3.12, lowest-direct, windows-latest)	3m 46s
checks / test (3.11, locked, ubuntu-latest)	46s
checks / test (3.13, lowest-direct, ubuntu-latest)	54s
checks / test (3.14, lowest-direct, windows-latest)	2m 16s
checks / test (3.14, locked, ubuntu-latest)	2m 24s
checks / test (3.14, locked, windows-latest)	3m 30s
checks / test (3.12, locked, windows-latest)	3m 19s
checks / test (3.11, locked, windows-latest)	2m 34s
checks / test (3.13, lowest-direct, windows-latest)	2m 38s
checks / test (3.13, locked, windows-latest)	2m 30s
checks / test (3.13, locked, ubuntu-latest)	46s
checks / test (3.10, locked, ubuntu-latest)	56s
checks / test (3.12, locked, ubuntu-latest)	54s
checks / test (3.12, lowest-direct, ubuntu-latest)	59s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 18s
all-green	5s
	39m 15s

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