feat: 初始化 Halo 暗色模式插件

- Halo Plugin 后端（Java/Gradle），含 DarkModePlugin 主类和测试
- Vue 3 + TypeScript 前端 UI，包含主题切换组件和设置页面
- 暗色模式 CSS 变量和覆盖样式（布局/编辑器/表单/滚动条等）
- 设计文档和调查文档
- Halo 插件/主题开发 Agent Skills

Co-Authored-By: Claude <noreply@anthropic.com>

.agents/skills/halo-plugin-dev/references/api-changelog.md

@@ -0,0 +1,29 @@
+# Plugin API Changelog
+
+Read the official changelog before using version-sensitive plugin APIs,
+upgrading Halo dependencies, or raising `spec.requires`.
+
+Official docs:
+
+- Plugin API changelog: https://raw.githubusercontent.com/halo-dev/docs/refs/heads/main/docs/developer-guide/plugin/api-changelog.md
+- Form schema: https://raw.githubusercontent.com/halo-dev/docs/refs/heads/main/docs/developer-guide/form-schema.md
+
+High-impact changes:
+
+| Halo version | Change                                                                                                                         | Skill reference                                                      |
+| ------------ | ------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------------------------------- |
+| 2.25.0       | `select` options support `icon` and `description`; remote selects support `requestOption.iconField` and `descriptionField`     | [ui-forms.md](ui-forms.md)                                           |
+| 2.25.0       | Plugin UI can register custom FormKit inputs through `definePlugin({ formkit: { inputs } })`                                   | [ui-entry.md](ui-entry.md), [ui-forms.md](ui-forms.md)               |
+| 2.25.0       | `secret` FormKit input supports `descriptionPreset`                                                                            | [ui-forms.md](ui-forms.md)                                           |
+| 2.23.0       | Spring Boot 4 upgrade can break plugins using Spring APIs; upgrade the Halo platform dependency and `spec.requires` together   | [devtools.md](devtools.md), [plugin-manifest.md](plugin-manifest.md) |
+| 2.23.0       | `iconify` supports optional `sizing` config                                                                                    | [ui-forms.md](ui-forms.md)                                           |
+| 2.22.8       | `toggle` FormKit input added                                                                                                   | [ui-forms.md](ui-forms.md)                                           |
+| 2.22.5       | SpringDoc update can break OpenAPI documentation generation; upgrade the Halo platform dependency and `spec.requires` together | [server-api.md](server-api.md), [devtools.md](devtools.md)           |
+| 2.22.2       | `switch` FormKit input added                                                                                                   | [ui-forms.md](ui-forms.md)                                           |
+| 2.22.0       | Custom model index/query APIs changed: use `IndexSpecs.single/multi`, `Queries`, and newer `ExtensionClient` query helpers     | [server-extension.md](server-extension.md)                           |
+| 2.22.0       | `@halo-dev/console-shared` was renamed to `@halo-dev/ui-shared`                                                                | [ui-shared.md](ui-shared.md)                                         |
+| 2.22.0       | Attachment selector extension results need `mediaType` on `AttachmentLike`                                                     | [ui-extension-points.md](ui-extension-points.md)                     |
+
+When a feature requires a newer Halo runtime, update dependency versions and
+`plugin.yaml` `spec.requires` together. Do not raise `spec.requires` for an
+optional UI enhancement unless the plugin cannot run without it.