Measure module depth as implementation size per exported symbol #18

Context

The history-based signals approximate module depth. Ousterhout's depth itself — how much implementation sits behind how much interface — needs the code: the size of a module's public surface against the size of its implementation.

Goal

For TypeScript/JavaScript modules, codeheat reports a depth ratio (implementation lines per exported symbol) so shallow modules with wide interfaces and little behind them stand out.

Acceptance criteria

• Exported symbols of a module's entry points are counted with the TypeScript compiler API (re-exports followed); implementation lines come from the existing metrics.
• The Report gains an additive per-module depth field, null for unsupported languages; documented in the schema and GLOSSARY.md.
• Tests cover a deep module (few exports, large implementation) and a shallow one.
• Bundle size and analysis time on a ~4,000-commit TypeScript monorepo are measured before and after and recorded in the pull request.

References

• Part of Roadmap: judge modularization and module depth #20; builds on module detection and entry points from Show module cohesion and cross-module coupling, aware of workspace packages #15 and Compare interface churn with implementation churn to spot shallow modules #16.