Polygon Labs Moves Bor and Heimdall Images to GHCR

Polygon Labs adds Bor and Heimdall container images to GHCR. Both clients publish to DockerHub and GHCR until 1st September 2026, then GHCR-only. Pull commands: `ghcr.io/0xpolygon/bor:vx.x.x`, `ghcr.io/0xpolygon/heimdall-v2:vx.x.x`. Update deployment pipelines now.