feat: add knowledge markdown formatting and detail retrieval

- Implemented KnowledgeWebsiteMarkdownPrompt for formatting webpage content into Markdown.
- Added GetItemDetail method in KnowledgeHandler to retrieve knowledge item details.
- Introduced KnowledgeDetailDrawer component for displaying knowledge item details in the admin web interface.
- Created MarkdownPreview component for rendering Markdown content.
- Added knowledge chunking and URL parsing logic to handle webpage content extraction and formatting.
- Updated database schema to include markdown_content in knowledge_items table.

server/migrations/20260405173000_add_markdown_content_to_knowledge_items.down.sql

@@ -0,0 +1,2 @@
+ALTER TABLE knowledge_items
+    DROP COLUMN IF EXISTS markdown_content;

server/migrations/20260405173000_add_markdown_content_to_knowledge_items.up.sql

@@ -0,0 +1,7 @@
+ALTER TABLE knowledge_items
+    ADD COLUMN markdown_content TEXT;
+
+UPDATE knowledge_items
+SET markdown_content = content_text
+WHERE markdown_content IS NULL
+  AND content_text IS NOT NULL;