fix: display original crawling URL in knowledge item edit modal

Fix issue where edit modal shows random crawled page URL instead of
the original URL provided by user when creating knowledge items.

Root cause: _transform_source_to_item() was using first_page_url
(random crawled page) instead of metadata.original_url (user input).

Changes:
- Use source_metadata.get('original_url') as primary URL source
- Fall back to first_page_url for backward compatibility
- Maintains existing behavior for legacy items without original_url

Before: Edit modal shows https://example.com/random-page-discovered
After:  Edit modal shows https://example.com (user's original input)

Fixes display issue in EditKnowledgeItemModal.tsx Source field.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

python/src/server/services/knowledge/knowledge_item_service.py

@@ -365,7 +365,7 @@ class KnowledgeItemService:
         return {
             "id": source_id,
             "title": source.get("title", source.get("summary", "Untitled")),
-            "url": first_page_url,
+            "url": source_metadata.get("original_url") or first_page_url,
             "source_id": source_id,
             "code_examples": code_examples,
             "metadata": {