fix: handle empty input and missing clipboard API in Format Prompt Values dialog

[sauravbaid3]

Problem

• When leaving the input field empty in the Format Prompt Values dialog and clicking on Copy to clipboard, the app:
  Throws a console error:
  TypeError: Cannot read properties of undefined (reading 'writeText')

• Turns the page blank

• Causes unsaved flow data to be lost

Root Cause

• navigator.clipboard.writeText was being called without checking if the Clipboard API was available
• Empty string values ("") were not being handled safely, leading to JSON parsing and clipboard issues

Solution

This PR improves clipboard handling across components by:

• Adding Clipboard API availability checks (if (navigator?.clipboard?.writeText))

• Wrapping copy operations in try/catch blocks for safer error handling

• Gracefully handling empty values ("") without breaking the UI

• Applying the same safety pattern consistently across components:
  JsonEditor.jsx
  ExpandedChunkDialog.jsx
  NodeExecutionDetails.jsx

Result

No more crashes or blank pages when copying empty/invalid input
Consistent clipboard handling across the app
Better browser compatibility and error resilience