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Add a logo, favicon and banner (#9) #27

Job	Run time
ty	51s
maturin build (abi3) + fresh-venv install	28s
cargo test / clippy / fmt	37s
pytest 3.11	47s
pytest 3.13	35s
ruff	8s
pytest 3.12	35s
differential vs ruamel (reported, non-blocking)	35s
	4m 36s