build

docs and readme: add the new `jj` logo #18821

Job	Run time
build (ubuntu-24.04)	45s
Build without Git support	44s
cargo-deny (advisories)	23s
build (macos-13)	44s
build (macos-14)	42s
cargo-deny (bans licenses sources)	22s
build (windows-latest)	29s
build (ubuntu-24.04, --all-features)	45s
Run doctests	44s
Check protos	32s
Clippy check	44s
Codespell	12s
Check that MkDocs can build the docs	10s
Check that MkDocs can build the docs with latest Python and uv	14s
Check formatting	19s
	7m 49s

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