bug: grant license detection mode conflicts with syft license scanner

### Summary
Syft needs a way where we can inject the scanner via API rather than injecting a config that then creates the scanner. It's either this or syft needs to expose a way to retrieve the scanner from context that it's using so grant can share the same scanner during its own license analysis.

No files or tests are named. Start by tracing how grant's license analysis and Syft's license scanner are constructed and passed through context. Compare the two alternatives in the issue—API injection or scanner retrieval from context—and define a single sharing path; done means grant's detection mode can share Syft's scanner without conflicting scanner creation.

Written by the indexing model from the issue text.