build: add beautifulsoup4 to dev dependencies for E2E tests

The test_files_page_e2e.py module requires BeautifulSoup for HTML parsing
and validation. This fixes the CI import error.

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

Co-Authored-By: Claude <[email protected]>

Author: patchmemory

pyproject.toml

@@ -25,6 +25,7 @@ dev = [
   "pytest-playwright==0.4.3",
   "playwright==1.40.0",
   "requests>=2.32",
+  "beautifulsoup4>=4.12",
 ]
 
 # Optional LLM provider (only needed if you enable Graphrag LLM features)