Neo4j property-graph projection and graph.cypher snapshot writer #34

Add a live-database writer that pushes the projected graph over Bolt and updates
only what changed, so re-analysis is incremental rather than a full rewrite.

Scope:

• codeanalyzer/neo4j/bolt.py: lazy neo4j-driver import (optional dependency)
• per-module content-hash diff; rewrite only changed modules
• delete edges owned by changed modules; detach-delete vanished declarations
• full-run orphan prune for modules whose source file was removed
• CLI: --emit neo4j --neo4j-uri bolt://... (requires the [neo4j] extra)