[Feature] GitHub Code Skimming for Decomposer Grounding

[Ash-Blanc]

Enhance the Decomposer phase to support GitHub repository skimming for better technical grounding.

Key Requirements:

• Detect GitHub URLs associated with papers (already partially supported in models, but not used in pipeline).
• Implement a 'GitHub Skimmer' tool/step that fetches README and core implementation primitives.
• Ground the Decomposer's 'Technical Primitives' output in both paper claims and actual code evidence.