Add optional Tone field to Sites for AI content generation

- Add tone column to sites table (nullable string)
- Add TONES constant to Site model with predefined options:
  professional, casual, technical, friendly, formal, humorous,
  conversational, authoritative, inspirational, educational, minimal, detailed
- Update Sites Livewire component to edit tone
- Update Sites view with tone select dropdown in form
- Add tone column to sites table display
- Add tone to SiteResource API response

AI agents can now read the site's tone and use it when generating content.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

app/Http/Resources/SiteResource.php

@@ -18,6 +18,7 @@ class SiteResource extends JsonResource
             'wp_username' => $this->wp_username,
             'wp_app_password' => $this->wp_app_password,
             'api_instructions' => $this->api_instructions,
+            'tone' => $this->tone,
             'created_at' => $this->created_at,
             'updated_at' => $this->updated_at,
         ];