Update vulnerability severity color scheme for improved visual hierarchy

[Copilot]

The vulnerability display used inconsistent colors that didn't provide clear visual distinction between severity levels (critical and high were both red variants, medium was yellow, low was green).

Changes

Updated color mappings in secator/output_types/vulnerability.py:

colors = {
    'critical': 'red',           # was: 'bold red'
    'high': 'dark_orange',       # was: 'red'
    'medium': 'orange',          # was: 'yellow'
    'low': 'cyan',              # was: 'green'
}

This creates a clearer gradient from red (critical) through orange tones (high/medium) to cyan (low), making severity levels immediately distinguishable in terminal output and reports.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>feat : Improve graph colors</issue_title>
<issue_description>Make sure the colors in the WorkspaceDetails component's vulnerability graphs reflect the label values:

• critical --> red
• high --> dark orange
• medium --> orange
• low --> real
  </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes feat : Improve graph colors #847

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