feat(styleguides): add sql style guide asset

[KelbyBahr]

Summary

Adds a standardized sql.md style guide asset to skills/conductor-setup/assets/code_styleguides/.

Motivation

When running /conductor:conductor-setup on SQL-centric projects (such as dbt or data warehouse pipelines), Conductor did not have a built-in SQL style guide asset available in its assets catalog. This addition provides a baseline style guide covering lowercase keywords, CTE structures, explicit aliasing, and semantic view standards.

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