feat(chat): add toast notification system and docker AI config

- Add global Toast component with success/error/warning/info types
- Create toastStore using Svelte 5 runes for centralized notifications
- Add GOOGLE_GENAI_API_KEY to mana-core-auth docker-compose config

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

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

docker-compose.dev.yml

@@ -68,6 +68,7 @@ services:
       CORS_ORIGINS: ${CORS_ORIGINS:-http://localhost:3000,http://localhost:5173,http://localhost:8081}
       CREDITS_SIGNUP_BONUS: ${CREDITS_SIGNUP_BONUS:-150}
       CREDITS_DAILY_FREE: ${CREDITS_DAILY_FREE:-5}
+      GOOGLE_GENAI_API_KEY: ${GOOGLE_GENAI_API_KEY}
     depends_on:
       postgres:
         condition: service_healthy