tokmd-analysis-maintainability 1.9.0

Maintainability index scoring and Halstead integration for tokmd analysis.
Documentation
# tokmd-analysis-maintainability

Maintainability scoring helpers for tokmd analysis receipts.

## Problem

You want maintainability metrics derived from complexity and size without
re-implementing the scoring math in the caller.

## What it gives you

- `compute_maintainability_index`
- `attach_halstead_metrics`

## Integration notes

- Uses the simplified or full SEI-style formula depending on Halstead volume.
- Recomputes the index only when the existing complexity report already has a
  maintainability slot and Halstead volume is positive.
- Keeps the Halstead merge logic local to the analysis layer.

## Go deeper

### Reference

- [Source]src/lib.rs
- [tokmd-analysis-halstead]../tokmd-analysis-halstead/README.md

### Explanation

- [Architecture]../../docs/architecture.md
- [Philosophy]../../docs/explanation.md