Jonathan/cmake2bazel heuristic cost estimator

[jonathan-engflow]

Summary

Adds aheuristic migration cost estimator for CMake-to-Bazel conversions.

• Estimates engineering hours from the extracted CMake model and optional parity diff
• Supports optional hourly-rate and token-pricing inputs
• Adds runnable example model and diff artifacts
• Documents the estimation step in the skill and README
• Adds focused estimator tests

Validation

• python3 tests/test_engine.py
• python3 tests/test_extractors.py
• python3 tests/test_triage.py
• python3 tests/test_configure.py
• python3 tests/test_estimate_cost.py

Notes

This is an initial heuristic, not a fixed quote. DIFF_HOURS is intentionally visible for future calibration against completed migrations.