fix(zipsign): update zipsign API to v0.2 + fix critical panic

Merge PR #429

This PR includes:
1. Zipsign API update from v0.1.5 to v0.2.0 (Issue #421)
2. Critical panic fix for terraphim-agent TUI startup (Issue #439)

All changes verified with disciplined-verification and disciplined-validation skills.
- Build: ✅ Clean
- Format: ✅ Passes cargo fmt
- Functional: ✅ No panic, runs cleanly
- Acceptance: 5/5 criteria met
- Production ready: ✅ Approved

Co-Authored-By: Terraphim AI <noreply@terraphim.ai>

Author: AlexMikhalev