fix: remove broken extern c from config-shape, add missing use types

Summary

Fix two broken examples that fail zero check on current main:

1. examples/config-shape.0: Remove broken extern c declarations that cause CGEN004 (unsupported backend type). The extern syntax for C FFI is not supported by the direct Mach-O backend.

2. examples/systems-package/src/helpers.0: Add missing use types import needed for Status type resolution.

Validation

# Before: both files produce diagnostics
zero check --json examples/config-shape.0        # CGEN004
zero check --json examples/systems-package/       # NAM003 (Status unknown)

# After: both clean
zero check --json examples/config-shape.0         # 0 diagnostics
zero check --json examples/systems-package/       # 0 diagnostics

Changes

• examples/config-shape.0: Removed 6 lines (extern c, extern type)
• examples/systems-package/src/helpers.0: Added 2 lines (use import)