Test Coverage Targeter

Builds a "what to test next" recommendation by combining a coverage report (LCOV / Cobertura / coverage.py JSON / Jest JSON / JaCoCo XML) with the PR's `git diff`, ranking uncovered branches by risk × cost - risk weighted by McCabe cyclomatic complexity and code-churn frequency, cost weighted by the unit-test pyramid layer (unit tests cheaper than integration than E2E). Also carries the coverage debt ledger: a weekly per-file drift report over N historical main runs flagging `falling` (line% slid >M pp from peak), `stale` (flat coverage + high churn), and `orphan` (lost last covering test) files, whose rows feed the same targeting. Emits a prioritized list with concrete f…