docs: clarify casing behavior and document config option

[CollegeRideOut]

Summary

Adds documentation improvements around the casing option to clarify its behavior and usage across Drizzle ORM and drizzle-kit.

Changes

• Clarifies that the casing option in the Drizzle ORM instance only affects runtime query mapping
• Adds a note explaining that drizzle-kit uses its own separate configuration
• Documents the casing option in drizzle.config.ts, which was previously not included in the config reference
• Adds a cross-link between ORM docs and drizzle-kit config docs for better discoverability

Motivation

There is recurring confusion around how casing behaves between the ORM and drizzle-kit, as seen in multiple issues.
This PR aims to make that separation explicit and reduce potential misunderstandings.

Related

• Docs are misleading for casing #609
• [BUG]: drizzle-kit generate does not respect snake_case config drizzle-orm#5366

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Happy to adjust wording or placement if there’s a preferred style for this section.

This pull request was drafted with the help of AI tools. All content has been reviewed and validated by me, including checking against the configuration and current documentation for correctness.