fix(gateway): validate ZT domain inputs

[kvinwang]

Problem

ZT domain inputs were used as DNS/state keys before canonical syntax validation. Empty, malformed, or non-canonical names could create unusable records and inconsistent lookup keys.

Root cause and fix

Validate the domain at the API boundary and only persist a canonical domain representation.

Implementation

The branch records the following focused implementation work:

• fix(gateway): validate ZT domain inputs

Changed paths:

• dstack/gateway/src/admin_service.rs

Scope

This PR addresses one logical gateway finding. It intentionally excludes the acceptance-test infrastructure from #841 and unrelated product fixes from #840.

Dependency and merge order

This PR is based directly on master and does not require another split product PR to merge first.

Verification

• git diff --check origin/master..origin/codex/fix-gateway-zt-domain-inputs: passed.
• The declared base was verified as an ancestor of the PR head.
• Focused compile/check verification was run for the changed component where applicable; non-Rust packaging or configuration changes were reviewed against their exact branch delta.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.