Replace node-agent with Better Stack eBPF agent

[paweljw]

Summary

• consume ghcr.io/betterstackhq/ebpf-agent:0.1.3 as a source image and copy its binary into the collector eBPF image
• remove the Coroot node-agent source build, patches, and patch-only CI workflow
• update component version checks and runtime documentation for the replacement

Verification

• built the complete collector eBPF image locally using the verified ebpf-agent build from PR Add Prometheus Node Exporter #79
• confirmed the embedded binary checksum matches the source-layer binary
• confirmed /usr/local/bin/ebpf-agent is executable and /usr/local/bin/node-agent is absent
• parsed all GitHub workflow YAML and verified the Dockerfile/documentation version pin is 0.1.3

Collector CI must additionally verify authenticated private GHCR access and both target architectures.