resolveAnalyzerRepoMap

Returns the analyzer's --repo NAME=PATH map: every DSL-configured repo (under stigProject { repos { … } }) whose implementationRoot resolves to a directory on disk. Falls back to a single entry { rootProject.name → rootDir } when no repos are configured so single-repo projects work with zero DSL setup.

Paths are absolute. The C++ analyzer normalizes them to repo-relative sourceRepo/sourceFile pairs at emit time and re-emits the top-level repos[].path relative to the analysis JSON's directory for cross-machine byte-identical output.