UI improvements: fix translation and custom icons for schedule trigger

[lyzno1]

Summary

This PR includes two UI improvements:

1. Fix translation: Correct Start tab translation in workflow node selector from 'User Input' to 'Start'
2. Custom icons: Add custom asterisk and calendar icons for schedule trigger mode toggle with proper sizing

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[lyzno1]