fix(scanner): normalize redundant SPDX match parentheses

[mstykow]

Summary

• normalize public license_expression_spdx rendering for detections and nested matches so redundant top-level parentheses are removed consistently
• add a regression test covering (MIT OR CC0-1.0) at both detection and match level
• keep the fix scoped to the scanner conversion boundary, reusing the existing SPDX combiner instead of changing internal detection behavior

Scope and exclusions

• Included: src/scanner/process/license.rs and src/scanner/process/license_test.rs
• Explicit exclusions: no changes to internal license detection generation, no golden fixture updates, and no broader output-schema refactors