docs: add multi-tenancy guide, example server, and OAuth e2e tests #46

Job	Run time
checks / pre-commit	36s
checks / readme-snippets	12s
checks / test (3.10, locked, ubuntu-latest)	53s
checks / test (3.13, locked, ubuntu-latest)	49s
checks / test (3.14, lowest-direct, windows-latest)	2m 46s
checks / test (3.10, lowest-direct, windows-latest)	2m 35s
checks / test (3.10, locked, windows-latest)	2m 28s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 1s
checks / test (3.12, lowest-direct, ubuntu-latest)	54s
checks / test (3.14, locked, ubuntu-latest)	2m 16s
checks / test (3.12, locked, ubuntu-latest)	56s
checks / test (3.11, lowest-direct, windows-latest)	2m 46s
checks / test (3.13, lowest-direct, windows-latest)	3m 1s
checks / test (3.13, locked, windows-latest)	2m 30s
checks / test (3.12, locked, windows-latest)	3m 8s
checks / test (3.11, lowest-direct, ubuntu-latest)	53s
checks / test (3.13, lowest-direct, ubuntu-latest)	53s
checks / test (3.14, locked, windows-latest)	3m 2s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 11s
checks / test (3.11, locked, ubuntu-latest)	49s
checks / test (3.12, lowest-direct, windows-latest)	3m 19s
checks / test (3.11, locked, windows-latest)	2m 25s
all-green	5s
	39m 28s

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