fix: enhance chat reference links and prevent text overflow (#173)

This commit addresses two related issues in the chat interface:

1. **Fix broken reference links (OSS-310)**
   - Completely rewrote convertReferencesToMarkdownLinks() with greedy pattern matching
   - Now handles all edge cases: references after commas, nested brackets, bold markdown
   - Added visual icon indicators (FileText, Lightbulb, FileEdit) for reference types
   - Implemented proper error handling with toast notifications
   - Added validation for reference types and ID lengths

2. **Fix long URL/text overflow (#172)**
   - Added break-words and overflow-wrap classes to chat messages
   - Long URLs and text now wrap properly within chat bubbles
   - Applied fix consistently across source chat, notebook chat, and search results

**Technical Details:**
- Enhanced reference detection algorithm processes from end to start to preserve indices
- Context analysis (50 chars before/after) determines original formatting
- Icons are 12px, accessible, and themed appropriately
- All changes pass linting and build successfully

**Files Modified:**
- frontend/src/lib/utils/source-references.tsx (core algorithm rewrite)
- frontend/src/components/source/ChatPanel.tsx (error handling + text wrapping)
- frontend/src/components/search/StreamingResponse.tsx (error handling + text wrapping)
- open_notebook/utils/token_utils.py (ruff formatting fix)

fixes #172

open_notebook/utils/token_utils.py

@@ -4,6 +4,7 @@ Handles token counting and cost calculations for language models.
 """
 
 import os
+
 from open_notebook.config import TIKTOKEN_CACHE_DIR
 
 # Set tiktoken cache directory before importing tiktoken to ensure