Chore/validate booking create

[eugbyte]

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[Copilot]

Pull Request Overview

This pull request contains various UI/UX improvements and bug fixes for the Evently application, including replacing inline SVG with icon components, styling updates, and adding duplicate booking validation.

• Replaces inline SVG search icon with Iconify icon component for consistency
• Updates email ticket template with improved styling and layout
• Adds validation to prevent duplicate bookings for the same gathering and account

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/evently.client/src/routes/gatherings/index.tsx	Replaces inline SVG search icon with Iconify icon component
src/evently.client/src/routes/__root.tsx	Minor CSS class reordering
src/evently.client/src/lib/components/navbar.tsx	Updates button sizes and styling for mobile navigation
src/Evently.Server/Program.cs	Adds global exception handler middleware
src/Evently.Server/Features/HealthChecks/HealthChecksController.cs	Adds test endpoint for error middleware
src/Evently.Server/Features/Emails/Views/Ticket.razor	Major redesign of email ticket template with improved styling
src/Evently.Server/Features/Bookings/Services/BookingService.cs	Adds duplicate booking validation
src/Evently.Server/Features/Bookings/BookingsController.cs	Fixes content type for HTML preview response
src/Evently.Server/Common/Middlewares/GlobalExceptionHandler.cs	Simplifies exception handling logic

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