[FEATURE] Add config file support for certificate pins

[chizy7]

Summary

Add runtime configuration file support for certificate pins to complement existing hardcoded defaults.

Motivation

• Enable pin updates without recompilation in production
• Support emergency certificate rotations
• Allow environment-specific pins (dev/staging/prod)

Proposed Solution

Implement hybrid approach in CertificatePinner::initializeDefaultPins():

1. Try loading from config/certificate_pins.json first
2. Fall back to hardcoded pins if file doesn't exist
3. Maintain backward compatibility

Implementation Notes

• Documentation already covers this approach (CERTIFICATE_PINNING.md:108-130)
• Keep hardcoded pins as safe defaults
• Add JSON schema validation for config file

Phase

Phase 4 - Production Deployment

References

• core/utils/CertificatePinner.cpp:166-187
• docs/security/CERTIFICATE_PINNING.md