GitLab repository URLs with nested groups/subgroups are rejected by validator

The gitlabURLRegex in internal/validators/utils.go only allows two path segments (owner/repo), rejecting valid GitLab URLs with subgroups.

Current:
^https?://(www\.)?gitlab\.com/[\w.-]+/[\w.-]+/?$
Fix:
^https?://(www\.)?gitlab\.com/[\w./-]+/[\w.-]+/?$

Example: https://gitlab.com/myorg/team/subgroup/my-mcp-server → invalid repository URL.

GitLab subgroups are a standard feature used in GitLab Enterprise. The current regex is preventing self-hosted registries from publishing servers whose source lives in a GitLab group hierarchy.

Start in internal/validators/utils.go and inspect gitlabURLRegex. Update validation so GitLab URLs containing nested groups and subgroups are accepted while the existing repository URL shape remains valid; verify the provided nested URL is no longer rejected.