Update documentation to reflect the actual JSON-based configuration
system instead of the old INI-style format.
Changes:
- Updated Quick Start section to reference config.example.json
- Rewrote Configuration section with JSON examples
- Added detailed environment variable override documentation
- Included CI/CD usage examples
- Documented all supported environment variables
All acceptance criteria from Issue #6 verified:
✓ config.example.json created and documented
✓ load-config.sh correctly parses JSON
✓ Environment variables take precedence over JSON
✓ Validation script catches missing required fields
✓ Documentation clear for new developers
✓ CI can inject credentials via env vars
Related: #6
