docs: add multi-tenancy guide, example server, and OAuth e2e tests #49

Job	Run time
checks / readme-snippets	11s
checks / pre-commit	21s
checks / test (3.10, lowest-direct, ubuntu-latest)	55s
checks / test (3.10, lowest-direct, windows-latest)	2m 24s
checks / test (3.13, lowest-direct, ubuntu-latest)	54s
checks / test (3.13, locked, windows-latest)	2m 11s
checks / test (3.14, locked, windows-latest)	3m 16s
checks / test (3.11, lowest-direct, ubuntu-latest)	53s
checks / test (3.10, locked, windows-latest)	2m 10s
checks / test (3.10, locked, ubuntu-latest)	49s
checks / test (3.14, locked, ubuntu-latest)	2m 20s
checks / test (3.11, locked, ubuntu-latest)	54s
checks / test (3.12, lowest-direct, windows-latest)	4m 13s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 1s
checks / test (3.12, locked, windows-latest)	3m 37s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 12s
checks / test (3.11, lowest-direct, windows-latest)	2m 32s
checks / test (3.11, locked, windows-latest)	2m 22s
checks / test (3.12, locked, ubuntu-latest)	58s
checks / test (3.13, locked, ubuntu-latest)	43s
checks / test (3.14, lowest-direct, windows-latest)	2m 19s
checks / test (3.13, lowest-direct, windows-latest)	2m 46s
all-green	3s
	39m 4s

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