`npm test` runs Jest but no watch-mode guide in CONTRIBUTING

[mercy60]

Internal ID: #92

Imported from ISSUES.md via scripts/import-issues.mjs.

Problem Statement. CONTRIBUTING.md does mention npm run test:watch; good. But no instructions to run jest filters by path.

Expected Outcome.

• Add Testing Strategies to CONTRIBUTING.

Files / modules affected.

• CONTRIBUTING.md

Dependencies. None.

Difficulty / Effort. Easy / XS (≈ 1 hour).

Labels. docs, testing