fix(domain): allow single-label hostnames without a TLD

[narcisonunez]

What is this PR about?

Regression from #4729: VALID_HOSTNAME_REGEX required at least one dot, rejecting single-label hosts like "dokploy-server", the TLD is optional.

Checklist

Before submitting this PR, please make sure that:

• You created a dedicated branch based on the canary branch.
• You have read the suggestions in the CONTRIBUTING.md file https://github.com/Dokploy/dokploy/blob/canary/CONTRIBUTING.md#pull-request
• You have tested this PR in your local instance. If you have not tested it yet, please do so before submitting. This helps avoid wasting maintainers' time reviewing code that has not been verified by you.

Issues related (if applicable)

closes #4881

Screenshots (if applicable)

Greptile Summary

This PR restores support for valid single-label hostnames by making the dotted-label portion of the hostname regex optional.

• Accepts names such as dokploy-server, localhost, and example.
• Adds regression tests while preserving rejection of malformed labels, underscores, spaces, and empty hostnames.

Confidence Score: 5/5

The PR appears safe to merge with no actionable defects identified.

The quantifier change narrowly permits a hostname without a dot while retaining the existing per-label character, length, and boundary restrictions, and the tests directly cover the intended regression.

_{Reviews (1): Last reviewed commit: "fix(domain): allow single-label hostname..." | Re-trigger Greptile}