Fix theme name validation in MCP tools

[ruibaby]

Theme tools reject names containing uppercase characters, such as
theme-echoCraft, with themeName must be a lowercase DNS label.

Replace DNS-label validation with non-empty string validation when updating
theme settings and reading templates. Preserve exact active-theme matching,
configuration version checks, and template path protections.

Fixes #16

Reproduction and verification:

• With theme-echoCraft as the active theme in the test fixture, updating a
  setting group or reading an HTML template fails before the fix.
• Both regression cases pass after the fix. Blank names and names whose case
  differs from the active theme remain rejected.

Validation:

• ./gradlew test --tests run.halo.mcpserver.tools.ThemeSettingToolsTest --tests run.halo.mcpserver.tools.ToolSupportTest -x processUiResources
  — 20 tests passed.
• git diff --check — passed.
• No end-to-end validation against a running Halo instance.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-15T16:28:16.948669Z	c4e5c1a	PR opened

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