Add Neo4j Cypher export (--neo4j)

[thunderstornX]

Summary

Adds a --neo4j export that serializes the maigret graph (the same one --graph builds) into a Cypher script importable into Neo4j, per #2630 and your go-ahead there.

Closes #2630

What it does

maigret <username> --neo4j writes a *_neo4j.cypher file. It reuses the existing MaigretGraph (the structure behind --graph), so it captures the same username / account / site / data nodes and relationships, and serializes them as idempotent Cypher:

• each node is MERGEd on a unique name (re-imports do not create duplicates),
• edges become [:LINKED_TO] relationships,
• with a CREATE CONSTRAINT ... IF NOT EXISTS on the node name.

No new runtime dependency (networkx is already used). Import with cypher-shell -u neo4j -p <pw> < <file>.cypher, or paste into the Neo4j Browser.

Refactor

I extracted the graph-building out of save_graph_report into a shared _build_maigret_graph() helper so both --graph and --neo4j use it; save_graph_report behavior is unchanged.

Testing

• Full pytest suite passes. Added tests/test_report.py::test_generate_neo4j_report (covers the Cypher structure plus escaping of quotes and newlines) and updated tests/test_cli.py's arg baseline for the new flag. No regressions; --graph still works.
• Live import: generated the Cypher from a real scan and imported it into Neo4j 5 with zero errors (25 nodes / 26 relationships; idempotent on re-import).
• Docs: added --neo4j to the README usage block and docs/source/command-line-options.rst.

Note: the CREATE CONSTRAINT ... IF NOT EXISTS FOR ... REQUIRE line uses Neo4j 4.4+ syntax; the MERGE statements keep the import idempotent on any version.

[thunderstornX]

[soxoj]

@thunderstornX amazing job, thanks a lot for an amazing contribution!
Sorry for the delay, I needed time to test it 👍
Feel free to improve this functionality further!

[thunderstornX]

thank you for your support and guidance, I will try to contribute more, I Just completed my Masters and am Looking for opportunities, feel free to visit my profile and throw any openings :) i will be thankful