fix: settings UI consistency — empty states, MCP layout, remove power…

[yujiangtao3456]

… section

1. AIModelConfig: empty model list now uses --element-bg-subtle background instead of transparent, matching other ConfigPageSection body styles
2. BasicsConfig: remove BasicsPreventSleepSection (电源) — not applicable on OHOS
3. McpToolsConfig:
   • Remove .bitfun-collection-empty override (was flex-start + no padding; now uses standard centered style)
   • JSON editor: add horizontal padding (-gap-3) for content margin
   • JSON actions: right-align (flex-end) instead of centered
4. ExternalSourcesConfig: __mcp-empty now centered with proper padding (-gap-6 -gap-4) instead of grid with no horizontal padding
5. VoiceInputConfig: __empty now centered with standard padding
6. AcpAgentsConfig: __empty now centered with standard padding

Summary

Fixes #

Type and Areas

Type:

Areas:

Motivation / Impact

Verification

Reviewer Notes

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.