fix: don't treat image namespace as registry

[JamBalaya56562]

Problem

SplitDockerImage treats everything before the first / as the registry. For Docker Hub images that use a namespace/user prefix — e.g. tianon/centos — this incorrectly yields Registry="tianon", Repository="centos" instead of Registry="" (implicit Docker Hub) and Repository="tianon/centos".

Per Docker's reference parser, the first path component is a registry only when it contains a . or :, or is exactly localhost. Otherwise it belongs to the repository path.

Change

SplitDockerImage now applies that rule: the first segment is treated as the registry only when it contains ./: or equals localhost; otherwise the whole user/image is kept as the repository. Tag parsing is unchanged.

Because DockerImage.String() rejoins registry + "/" + repository, the full image string still round-trips — only the split .Image.Registry / .Image.Repository fields change, which is the intended correction for templates that read those fields.

Tests

Added tianon/centos and tianon/centos:7 cases. All existing cases (ubuntu, custom.registry/…, localhost:8888/…, etc.) still pass. No new dependencies.

Fixes #154

🤖 Generated with Claude Code

[buchdag]

@JamBalaya56562 please flag AI-generated PR explicitly in the PR description (ie "🤖 Generated with Claude Code" like in this PR) and add the AI agent as co-author of the commits.

[JamBalaya56562]

Done — added the Co-Authored-By: Claude Opus 4.8 trailer to the commit and the 🤖 Generated with [Claude Code](https://claude.com/claude-code) note to the PR description. I also rebased onto the latest main. Thanks for the review!

[Copilot]

Pull request overview

This pull request corrects SplitDockerImage so Docker Hub namespaced images like user/repo are no longer misparsed as having a registry, aligning parsing with Docker’s reference rules.

Changes:

• Treat the first path segment as a registry only when it contains . or :, or equals localhost.
• Keep tag parsing behavior the same while adjusting how registry/repository are split.
• Add test cases covering Docker Hub namespaced images (tianon/centos with and without a tag).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
internal/dockerclient/docker_cli.go	Updates image-splitting logic to distinguish registries from Docker Hub namespaces.
internal/dockerclient/docker_cli_test.go	Adds coverage for namespaced Docker Hub images and round-trip stringification.

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