Relative timeframe validation not working correctly

[lucafwp]

Describe the bug

When selecting a relative timeframe the text validation accepts string clearly not valid

To Reproduce

Steps to reproduce the behavior:

1. Create a new time frame
2. Check "Relative start"
3. Insert following text as Start: -2 banana
4. Check "Relative end"
5. Insert following text as End: -1 banana
6. Create a report using newly created Timeframe
7. Generate the report

Expected behavior

Validation should accept only valid strings.

Screenshots

Your Environment

• Module version: 1.0.2
• Dependent module versions:
  ** icinga-php-library: 0.13.2
  ** icinga-php-thirdparty: 0.12.1
• Icinga Web 2 version and modules (System - About): 2.12.1
• Web browser and version: Chrome Version 125.0.6422.141
• Icinga 2 version used (icinga2 --version): 2.14.2-1
• PHP version used (php --version): 8.3.6
• Server operating system and version: Ubuntu 24.04