test: add 47 negative security tests for adversarial scenarios

Comprehensive adversarial test coverage targeting vulnerabilities
identified during post-MSRC security audit:

- Delegation depth abuse and Sybil resistance
- Wildcard capability delegation constraints
- Plugin path traversal rejection
- Ed25519 signature verification robustness (empty, truncated, wrong key)
- Handshake trust score manipulation resistance
- Identity lifecycle attacks (revoked, suspended, expired)
- Plugin signature bypass scenarios
- Challenge accumulation and expiry
- DID format injection
- Registry adversarial usage
- TrustBridge with missing/empty inputs

All 47 tests pass, 1852 total suite passes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: imran-siddique