Add contributor test matrix

[silentgeckoaudit3801]

Closes #64

Summary

• add a contributor test matrix for Aegis SDK feature areas
• map compliance, RWA metadata, admin actions, investor reads, transaction receipts, and typed errors to unit, fixture, smoke, and integration expectations
• link the matrix from README and CONTRIBUTING

Validation

• Documentation-only change; reviewed the generated markdown and links through the GitHub contents API.
• No project dependencies or toolchains were installed or executed.