Fix the Go module path and README lead

[dnmacon]

What changed

• rename the Go module and internal imports to github.com/alignment-farm/substrate
• add the five-interface result near the README lead
• add related project links

Why

The published import path now matches the repository owner, so go install and package indexing can resolve it.

Checks

• make check
• go test -race ./...
• required secret scans
• git diff --check