Convert absolute paths to relative paths in MDX files

Changed all internal documentation links in MDX files to use relative paths:
- plugin-editor.mdx: /concepts/plugins → ../concepts/plugins
- plugin-kanban.mdx: /concepts/plugins → ../concepts/plugins
- plugin-charts.mdx: /docs/concepts/plugins → ../concepts/plugins
- plugin-markdown.mdx: /reference/api → ../reference/api, /concepts/plugins → ../concepts/plugins
- plugin-object.mdx: /ecosystem/objectql → ../ecosystem/objectql, /concepts/* → ../concepts/*

All MDX files now consistently use relative paths for internal documentation links.

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

docs/plugins/plugin-charts.mdx

@@ -283,6 +283,6 @@ const chartSchema: BarChartSchema = {
 
 ## Related Documentation
 
-- [Plugin System Overview](/docs/concepts/plugins)
+- [Plugin System Overview](../concepts/plugins)
 - [Lazy-Loaded Plugins Architecture](../concepts/lazy-loading)
 - [Package README](https://github.com/objectstack-ai/objectui/tree/main/packages/plugin-charts)

docs/plugins/plugin-editor.mdx

@@ -178,6 +178,6 @@ const editorSchema: CodeEditorSchema = {
 
 ## Related Documentation
 
-- [Plugin System Overview](/concepts/plugins)
+- [Plugin System Overview](../concepts/plugins)
 - [Lazy-Loaded Plugins Architecture](../concepts/lazy-loading)
 - [Package README](https://github.com/objectstack-ai/objectui/tree/main/packages/plugin-editor)

docs/plugins/plugin-kanban.mdx

@@ -422,6 +422,6 @@ const kanbanSchema: KanbanSchema = {
 
 ## Related Documentation
 
-- [Plugin System Overview](/concepts/plugins)
+- [Plugin System Overview](../concepts/plugins)
 - [Lazy-Loaded Plugins Architecture](../concepts/lazy-loading)
 - [Package README](https://github.com/objectstack-ai/objectui/tree/main/packages/plugin-kanban)

docs/plugins/plugin-markdown.mdx

@@ -189,7 +189,7 @@ npm install our-package
 2. Configure your settings
 3. Start building!
 
-For more information, see the [API Reference](/reference/api).
+For more information, see the [API Reference](../reference/api).
   `,
   className: 'prose prose-lg max-w-none'
 }
@@ -376,6 +376,6 @@ const markdownSchema: MarkdownSchema = {
 
 ## Related Documentation
 
-- [Plugin System Overview](/concepts/plugins)
+- [Plugin System Overview](../concepts/plugins)
 - [Lazy-Loaded Plugins Architecture](../concepts/lazy-loading)
 - [Package README](https://github.com/objectstack-ai/objectui/tree/main/packages/plugin-markdown)

docs/plugins/plugin-object.mdx

@@ -539,7 +539,7 @@ const dataSource = new ObjectQLDataSource({
 
 ## Related Documentation
 
-- [ObjectQL Integration](/ecosystem/objectql)
-- [Data Sources](/concepts/data-source)
-- [Plugin System Overview](/concepts/plugins)
+- [ObjectQL Integration](../ecosystem/objectql)
+- [Data Sources](../concepts/data-source)
+- [Plugin System Overview](../concepts/plugins)
 - [Package README](https://github.com/objectstack-ai/objectui/tree/main/packages/plugin-object)