fix: add missing packages to requirements.txt for HuggingFace Spaces

Adds agent-framework-core and duckduckgo-search to requirements.txt.
These were in pyproject.toml but missing from requirements.txt, causing:
- Advanced mode to fail with "agent-framework-core not found"
- Web search to be unavailable

Fixes #50

requirements.txt

@@ -7,6 +7,12 @@ pydantic-ai>=0.0.16
 openai>=1.0.0
 anthropic>=0.18.0
 
+# Multi-agent orchestration (Advanced mode)
+agent-framework-core>=1.0.0b251120
+
+# Web search
+duckduckgo-search>=5.0
+
 # HTTP & Parsing
 httpx>=0.27
 beautifulsoup4>=4.12