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Polish upstream-based bilingual README and add release downloads #3

Job	Run time
contract	3m 45s
test-linux-rust (workspace-crates, -p webcodex-admin -p webcodex-runner-config -p webcodex-core -...	2m 31s
test-linux-tooling	2m 31s
test-linux-rust (runner, -p webcodex-runner)	2m 8s
test-linux-rust (server, -p webcodex)	4m 0s
test-macos	0s
test-windows-core	0s
test-windows-package	0s
test-linux-arm64	0s
test-windows-runner	0s
test-windows-arm64	0s
test-windows	0s
test	4s
	14m 59s