fix(onboarding): auto-select first SSH key for better UX

- Auto-select first SSH key when available instead of requiring explicit selection
- Remove disabled placeholder option from dropdown
- Prevents confusing error when user clicks "Use Selected Key" without changing dropdown
- Improves onboarding flow by having a sensible default selection

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

resources/views/livewire/boarding/index.blade.php

@@ -264,7 +264,6 @@
                                 <div class="p-4 rounded-lg border border-neutral-200 dark:border-coolgray-400">
                                     <form wire:submit='selectExistingPrivateKey' class="flex flex-col gap-4">
                                         <x-forms.select label="Existing SSH Keys" id='selectedExistingPrivateKey'>
-                                            <option disabled selected value="">-- Select a Private Key --</option>
                                             @foreach ($privateKeys as $privateKey)
                                                 <option wire:key="{{ $loop->index }}" value="{{ $privateKey->id }}">
                                                     {{ $privateKey->name }}