A call through an injected interface dependency lands on the interface method, leaving the
implementation unreachable from the call site. When an interface has exactly one
implementing class, add a dispatches_to edge from each interface method to the matching
implementation method. Guarded to avoid false links: requires a real implements edge, a
single implementer, and a single case-sensitively same-named method; both ends must be C#;
0 or 2+ implementers emit nothing. Lives in graphify.csharp_dispatch as a registered
resolver.
