Add Pivotick static HTML export format to gen_graphml.py

[adulau]

Motivation

• Provide a simple static HTML export from gen_graphml.py so generated MISP galaxy graphs can be opened directly in a browser and viewed using the Pivotick visualization library without a separate build step.

Description

• Add to_pivotick_html(nodes, edges, pivotick_library_url) which serializes the graph into an embedded JSON payload and returns a self-contained HTML page that dynamically imports Pivotick as an ES module and boots it in viewer mode.
• Add a new pivotick-html output format to --output-format and map it to the .html extension in output_suffix.
• Add a --pivotick-library-url CLI option (defaulting to the Pivotick develop branch jsDelivr URL) so consumers can override the module URL used by the generated page.
• Wire the main output branch to write the generated Pivotick HTML while preserving existing graphml, dot, and json-graph behavior.

Testing

• Ran python -m py_compile tools/gen_graphml.py and the file compiled successfully.
• Ran python tools/gen_graphml.py --output-format pivotick-html -o /tmp/misp-pivotick.html --select-name ransomware --cross-cluster-matching value --no-existing-relationships and the tool printed a success message indicating the HTML was written (example: "pivotick-html graph written to /tmp/misp-pivotick.html with 3 galaxies and 2102 clusters.").

---

Codex Task