build

docs and readme: add the new `jj` logo #18811

Job	Run time
build (ubuntu-24.04)	4m 51s
build (macos-13)	4m 50s
Build without Git support	1m 15s
build (macos-14)	4m 19s
build (windows-latest)	4m 36s
Run doctests	2m 37s
build (ubuntu-24.04, --all-features)	4m 51s
Check protos	36s
Codespell	13s
Check formatting	18s
cargo-deny (advisories)	23s
Clippy check	2m 48s
cargo-deny (bans licenses sources)	26s
Check that MkDocs can build the docs	13s
Check that MkDocs can build the docs with latest Python and uv	10s
	32m 26s

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