Add test:contracts root alias and fix contract testing documentation

[coderabbitai]

Context

This issue tracks improvements to contract testing clarity and developer experience, flagged during PR review.

Related PR: #895
Related comment: #895 (comment)
Requested by: @cedoor

Issues to Address

1. Missing root alias: Unlike other contract scripts (compile:contracts, ciphernode:add), there's no convenient test:contracts script in the root package.json
2. Documentation inconsistency: crisp-contracts README claims tests use Forge/Foundry, but the package.json actually uses Hardhat
3. Unclear guidance: Main README lacks explicit instructions on running contract tests from the repository root

Expected Outcome

• Developers can run pnpm test:contracts from repository root
• Documentation clearly states contract tests use Hardhat
• Both READMEs include explicit instructions for running contract tests