refactor: route snapshot enum lookup through resolver

[ktjn]

Summary

• route registry snapshot enum dependency lookup through the common named-declaration resolver
• preserve exact-version resolution, projection dependency formatting, semantic fallback, and deterministic lock output

Validation

• uv run ruff format .
• uv run ruff check .
• uv run python ../.github/scripts/check_mypy_baseline.py --baseline mypy-baseline.txt -- uv run mypy src/modelable --no-error-summary --show-error-codes
• registry snapshot and semantic focused tests (127 passed)
• full suite serially: 3155 passed, 67 skipped

Reviewed by subagent: no findings.