Update Base Foundry repository references

[codeforester]

Summary

• Move Base, base-demo, and BanyanLabs GitHub references from codeforester to basefoundry.
• Update the base-demo installer defaults and CI Base clone URL.
• Move the Go module path to the new basefoundry GitHub coordinate.
• Add validation to catch stale codeforester GitHub references while leaving Java package names unchanged.

Validation

• ./tests/validate.sh
• CGO_ENABLED=0 go test ./...
• git diff --check

Fixes #86