Serve v2 docs at the site root, with permanent per-major paths #3747

Job	Run time
checks / pre-commit	57s
checks / docs	1m 0s
checks / readme-snippets	12s
checks / test (3.10, lowest-direct, windows-latest)	1m 38s
checks / test (3.12, locked, windows-latest)	2m 3s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 23s
checks / test (3.11, lowest-direct, windows-latest)	2m 0s
checks / test (3.12, locked, ubuntu-latest)	1m 40s
checks / test (3.13, locked, ubuntu-latest)	1m 19s
checks / test (3.10, locked, ubuntu-latest)	1m 34s
checks / test (3.14, lowest-direct, windows-latest)	1m 51s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 23s
checks / test (3.14, locked, ubuntu-latest)	1m 9s
checks / test (3.12, lowest-direct, windows-latest)	1m 50s
checks / test (3.14, locked, windows-latest)	3m 22s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 21s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 29s
checks / test (3.10, locked, windows-latest)	1m 58s
checks / test (3.11, locked, ubuntu-latest)	1m 21s
checks / test (3.13, lowest-direct, windows-latest)	2m 15s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 19s
checks / test (3.13, locked, windows-latest)	1m 51s
checks / test (3.11, locked, windows-latest)	1m 53s
all-green	3s
	36m 51s

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