Fix nutrition agent pet type validation and error handling

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Summary

This PR implements the two requested fixes to address the nutrition agent's hallucination issue with unsupported pet types:

Changes Made

• Added pet type validation before making API calls to prevent unnecessary 404 errors
• Modified error handling to detect 404 responses and provide appropriate "not supported" messages
• Updated system prompt to prevent agent hallucination for unsupported pet types

Technical Details

1. Pet Type Validation: Added SUPPORTED_PET_TYPES constant and validate_pet_type() function to check against the 6 supported pet types (cat, dog, lizard, snake, bird, hamster) before making API calls.

2. Enhanced Error Handling:

   • Pre-validation prevents API calls for unsupported pet types
   • Explicit 404 status code detection with appropriate messaging
   • Clear listing of supported pet types in error messages

3. Agent Behavior Improvements:

   • Updated system prompt to explicitly prevent hallucination for unsupported pets
   • All tool functions now check for "not supported" messages and return them directly
   • Order creation also validates pet types before processing

Root Cause Resolution

This addresses the core issue identified in the investigation:

• High 404 Error Rate: Eliminated by validating pet types before API calls
• Agent Hallucination: Prevented by explicit error handling and updated system prompt
• Service Architecture Flaw: Mitigated by client-side validation matching service capabilities

Testing

The agent will now:

• ✅ Return clear "not supported" messages for unsupported pet types (e.g., gecko, rabbit)
• ✅ List the 6 supported pet types when encountering unsupported requests
• ✅ Continue providing accurate recommendations for supported pet types
• ✅ Prevent fabricated product recommendations for unsupported pets

Fixes the 315 404 errors and agent hallucination pattern identified in the root cause analysis.