Add BGL2 vs Graph-v3 comparison document

Comprehensive evaluation covering:
- Vertex and edge descriptor differences
- Container selector status (BGL2: only vecS; graph-v3: 20+ traits)
- Adaptation mechanisms (traits vs CPO)
- Strengths/weaknesses of each library
- Algorithm availability (BGL2 complete, graph-v3 none)
- Property map approaches
- Code examples side-by-side

Author: pratzl

agents/bgl2_comparison_query.md

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+# Comparison with modernized boost graph library (BGL2)
+
+The original boost graph library (BGL1, located at `/home/phil/dev_graph/boost/libs/graph/`) has been 
+modernized to use C++20 (`BGL2`, located at `/home/phil/dev_graph/boost/libs/graph/modern/`).
+
+Compare and contrast BGL2 with the current library, making sure that the following topics are covered
+- The differences between the vertex and edge descriptors.
+- The ability to adapt to pre-existing graph data structures.
+- Strengths and weaknesses in the capabilities each library
+- Other areeas of interest in the design and flexibility for the libraries.
+
+Algorithms have not been implemented for graph-v3 and is a known limitation.
+
+Output the result to `aggents/bgl2_comparison_result.md`.