Add GraphML generator for galaxies/clusters with optional inferred links

[adulau]

Motivation

• Provide a single tool to export the entire repository of galaxies and clusters as a GraphML graph for visualization and analysis.
• Allow both existing explicit relationships and inferred relationships (value/synonym matches) to be examined without modifying source JSON files.

Description

• Add a new CLI script tools/gen_graphml.py which loads galaxies/*.json and clusters/*.json and emits a GraphML graph with galaxy nodes, cluster nodes, and membership (contains) edges.
• The tool includes explicit edges from cluster.related by default and can disable them with --no-existing-relationships.
• The tool can infer cross-galaxy edges by matching normalized cluster values or values+meta.synonyms via --cross-cluster-matching value or value-or-synonyms, and it only creates inferred links between different galaxy types.
• Adds CLI options for input directories and output path, uses simple normalization of terms, and writes GraphML using xml.etree.ElementTree to the specified output file.

Testing

• Performed static validation with python -m py_compile tools/gen_graphml.py, which succeeded.
• Ran the tool to produce a full export with --output /tmp/misp.graphml, which completed and printed a summary (wrote GraphML with 115 galaxies and 48744 clusters).
• Ran the tool with inferred matching via --cross-cluster-matching value-or-synonyms and it completed successfully producing a GraphML file.

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Codex Task