test(api): validate accent hex color parameter

[KrishnanshPuri]

Description

Fixes #1434

Pillar

• 🎨 Pillar 1 — New Theme Design
• 📐 Pillar 2 — Geometric SVG Improvement
• 🕐 Pillar 3 — Timezone Logic Optimization
• 🛠️ Other (Bug fix, refactoring, docs)

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[Aamod007]

Corrects accent validation test input from #ZZZZZZZ (7 chars -> wrong length) to #ZZZZZZ (6 chars -> proper length, invalid hex chars). More precise boundary test. 219/219 tests pass.

[github-actions]

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