Vary lint:js log message based on context

[agibson-godaddy]

Follow-up to #106 (comment)

This varies the log message based on whether we're running the build task.

QA

1. Run sake lint:js
   • Output doesn't mention building
   
2. Run sake build
   • Output mentions building / halting on errors
   

[Copilot]

Pull request overview

This PR improves user experience by varying the JavaScript linting log message based on execution context. When running sake lint:js directly, the message simply reports errors and warnings. When running as part of sake build, the message additionally mentions the --fail-on-lint-errors flag option, which is more relevant in the build context.

Changes:

• Added conditional logic to display context-appropriate log messages based on whether the linting is part of a build task

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