frontend: SettingsCluster stories for cluster settings states

[greedy-wudpeckr]

Summary

This PR adds comprehensive Storybook coverage for the SettingsCluster, increasing test coverage from 0% to full visual documentation across all component states including cluster settings form, save operations, error handling, and validation scenarios.

Related Issue

Fixes #4682

Steps to Test

• npm run frontend:storybook
• Go to Settings > SettingsCluster in the sidebar
• Test each story

[k8s-ci-robot]

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[Copilot]

Pull request overview

This PR adds comprehensive Storybook stories for the SettingsCluster component, fulfilling the requirements from issue #4682 to increase test coverage from 0% to full visual documentation. The stories demonstrate the cluster settings form across various states including form interactions, data persistence, error handling, and validation scenarios.

Changes:

• Created SettingsCluster.stories.tsx with 11 story variants covering all major component states
• Implemented a clean localStorage setup pattern using a helper function
• Configured comprehensive mock Redux store to support all component dependencies
• Added clear JSDoc documentation for each story explaining its purpose

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