Read imports and exports for Go #39

Context

Hidden coupling (#17) and module depth (#18) read imports and exports through one adapter per language; only TypeScript/JavaScript has one. Go's syntax makes this cheap: import blocks name package paths, a package is a directory, and exported identifiers are capitalized.

Goal

Go repositories get Coupling.imports and Module.depth like TypeScript repositories do.

Acceptance criteria

• A Go adapter (a lightweight scanner, no new native dependency) resolves import paths under the repository's go.mod module path to the package's universe files; imports of other modules are ignored.
• It lists a package's exported identifiers (capitalized top-level func, type, var, const) for depth.
• A fixture repository with an imported pair, a hidden pair, and a multi-module go.work layout proves both.

References

• Part of Read imports and exports beyond TypeScript and JavaScript #38. Builds on Flag hidden coupling: files that change together without importing each other #17 and Measure module depth as implementation size per exported symbol #18.