SparkyFitness: SSRF via unvalidated custom_url in AI service settings

SparkyFitness is a self-hosted, AI-powered health and fitness tracker for families. Prior to 1.6.0, SparkyFitnessServer/services/chatService.ts and SparkyFitnessServer/services/labelScanService.ts do not validate destinations supplied in custom AI service settings. An authenticated user saves a custom AI service URL and invokes an affected AI flow. The user can save a custom AI service URL and trigger an outbound request. Successful exploitation can send server-side POST requests with a controlled bearer value, probe internal services, and disclose the AI system prompt. This issue is fixed in version 1.6.0.