Returning an error string caused the bot to send "Lo siento, tengo
problemas para procesar tu mensaje" to the user whenever OpenAI/Gemini
was unavailable or misconfigured. Now it returns null so BotRouter can
fall back to the category greeting menu instead of sending the error.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
- Settings: agrega Gemini al selector de proveedor, campos gemini_api_key y gemini_model
- Modelos: gemini-2.0-flash, gemini-1.5-flash, gemini-1.5-pro
- AiBot::callGemini(): llama generateContent API con system_instruction y historial
- migrate.php: seed defaults gemini_api_key y gemini_model
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>