[Bug]: ExtractRegistryAndRepo mishandles digest-pinned refs and registries with ports

[Abhineshhh]

Version

sbi version: main @ d9404ec
OS: N/A (pure string-parsing bug)
Go: 1.26.5

What happened?

ExtractRegistryAndRepo splits on the first :, which breaks digest-pinned references and host:port registries:

Input	Actual	Expected
mcr.microsoft.com/dotnet/aspnet:8.0@sha256:abc	tag=8.0@sha256:abc	tag=8.0
mcr.microsoft.com/dotnet/aspnet@sha256:abc	repo ends with @sha256, tag=abc	clean repo, empty tag
localhost:5000/myrepo:1.0	reg=mcr.microsoft.com, tag=5000/myrepo:1.0	reg=localhost:5000, tag=1.0

This corrupts registry / repository / tag columns and can interact badly with UNIQUE(registry, repository, tag).

Expected: Parse like Docker references — strip @digest first; last : after last / is the tag; allow host:port registries.

Steps to reproduce

1. Call ExtractRegistryAndRepo with the inputs in the table above (unit test).
2. Observe incorrect registry / repository / tag fields.