Apply Drupal coding standards (PHPCS, PHPSTAN etc) fixes

Problem/Motivation

The GitLab continuous integration (CI) pipeline is showing warnings (https://git.drupalcode.org/project/nanobanana_editor/-/pipelines/670538) due to multiple global code quality issues, reported by various validation tools, such as cspell, eslint, phpcs, phpstan, and stylelint.

These warnings and errors appear throughout the module and prevent the pipeline from completing successfully.

This issue aims to perform a complete code quality cleanup across the entire module to align it with Drupal standards and the project's automated linting rules.

Steps to follow

1. Run the GitLab continuous integration pipeline or run the validation jobs locally:

• cspell .
• eslint.
• phpcs --standard=Drupal,DrupalPractice .
• phpstan analyze
• stylelint "**/*.css"

Proposed solution

Apply global code quality fixes across the entire repository:

• Correct spelling errors detected by cspell.
• Resolve JavaScript style and syntax issues detected by eslint.
• Apply Drupal coding standards using phpcbf and manually fix remaining phpcs issues.
• Address static parsing errors reported by phpstan.
• Correct CSS formatting and rules violations detected by stylelint.

After applying all fixes, rerun the pipeline to confirm that all validation jobs have completed successfully.