[AUDIT] Bare RuntimeError in template_loader

[rsionnach]

Severity: MEDIUM
File: src/nthlayer/specs/template_loader.py:77
Category: CLAUDE.md violation

template_loader raises bare RuntimeError: raise RuntimeError(f'Built-in templates directory not found: {templates_dir}'). Should use ConfigurationError from core/errors.py. As RuntimeError, it bypasses structured error handling and exit code system.

Fix: Replace with raise ConfigurationError(f'Built-in templates directory not found: {templates_dir}').

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Beads: trellis-i1u5