Use laravel/ai default provider for OpenRouter

[paulocastellano]

Summary

OpenRouter is a first-class provider in the Laravel AI SDK (docs): set OPENROUTER_API_KEY and use openrouter as the configured provider. No custom driver wiring is needed.

Our agents were blocking that path. Each one overrode provider() with:

match (config('ai.default')) {
    'openai' => Lab::OpenAI,
    'anthropic' => Lab::Anthropic,
    default => Lab::Gemini,
};

So AI_TEXT_PROVIDER=openrouter was remapped to Gemini. Per the SDK, when an agent omits provider(), Promptable already falls back to config('ai.default').

Changes

• Remove the duplicated provider() overrides from all AI agents.
• Gate text-AI availability (BrandAnalyzerRunner, shared aiEnabled) on ai.providers.{default}.key via App\Support\AiConfiguration.
• Document OPENROUTER_API_KEY / openrouter in .env.example.
• Add/update tests for OpenRouter availability and that agents no longer override provider().

Usage

AI_TEXT_PROVIDER=openrouter
AI_TEXT_MODEL=openai/gpt-4o-mini
OPENROUTER_API_KEY=sk-or-v1-...

Related: #216 (alternative approach that patches each match instead of using the SDK default).