Phase 4: goscan — Go analyzer born in the monorepo #13

Create goscan/, a Go-language analyzer built on core/ from day one. This is the validation of the whole extraction (rule of three): a new language should only need the adapter layer.

Blocked by Phase 2 (#8–#11); recommended after Phase 3 (#12) so the core API is proven by two adopters.

Adapter surface to implement (everything else comes from core)

• Parser adapter: go/ast (stdlib) → core/apted.TreeNode conversion + fragment extraction
• CFG builder for Go control flow (defer/goto/select/labeled break) targeting core/cfg.CFG
• StatementClassifier/NoOpClassifier, ComplexityContributor (short-circuit operators), Go CostModel, CommentStripper (//, /* */)
• Module resolution for the dependency graph (go.mod-aware imports; AbstractnessFunc = interface/exported ratio)
• Scoring policy: pick complexity/dead-code penalty formulas (start from jscan's count-ratio approach)
• CLI + report layer (reuse jscan's structure), goscan/vX.Y.Z release setup

Positioning notes

• Competitor gap: staticcheck/golangci-lint don't do clone detection or health scoring; dupl is weak — clone detection + health score is the differentiator
• Timing is a product decision: infrastructure cost is low after Phase 2/3, so this can wait for demand signal

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