refactor: remove Node.js setup and add bun caching in build workflow #2561

Job	Run time
Validate Build Configuration	3s
DockerHub README sync	-1s
Tests & Frontend Build (8.4)	1m 15s
Build Container (amd64)	41s
Build Container (arm64)	1m 3s
Publish multi-arch manifest	19s
	3m 20s

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