Feat/aura open design system polish

[altaskur]

Description

This PR introduces the new AuraOpen theme preset (based on PrimeNG Aura) and applies a full UI polish pass across the app to improve visual consistency, accessibility, and maintainability.

Goal

Replace the previous theme setup with a cleaner, scalable design-system implementation (AuraOpen), align app + Storybook theme behavior, and resolve quality gate blockers so the branch is ready for review.

Key Changes

• Migrated theme wiring from AuraBlack to AuraOpen in app and Storybook, including new semantic light/dark token configuration.
• Applied design-system polish across global styles, cards, dialogs, calendar, and home page to improve hierarchy, spacing, states, and consistency.
• Added/updated tests and addressed Sonar issues (including safer nullish coalescing usage) to pass quality gate and unblock CI/push.

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📝 Documentation update
• 🎨 Style/UI changes
• ♻️ Refactoring (no functional changes)
• ⚡ Performance improvement
• ✅ Test updates
• 🔧 Build/configuration changes

Impact Assessment

Database Impact

No database schema or migration changes.
No data transformation required.
No impact on existing persisted records.