refactor: centralize string normalization with trim_lower macro

[Ritik574-coder]

Summary

Introduced a reusable trim_lower macro to centralize string normalization logic across intermediate models. This removes duplicated LOWER(TRIM(...)) expressions, improves code readability, and makes future maintenance easier.

Changes made

• Added a reusable trim_lower macro in macros/trim_lower.sql
• Replaced repeated LOWER(TRIM(...)) expressions with the new macro
• Refactored customer, employee, inventory, product, return, review, and store intermediate models
• Improved code consistency and maintainability
• Updated .gitignore

Validation

• Commands tested locally (if applicable)
• Docs links checked
• No secrets committed
• CI passes

Related issues

N/A

Notes for reviewers

This is a refactoring change only. No business logic has been modified. The macro simply replaces repeated string normalization expressions, making the project easier to maintain and reducing code duplication.

[Ritik574-coder]

improve readability by extracting trim_lower macro