🔍 Add model validation on startup

[Gilfeather]

Description

Add comprehensive model validation during server startup to catch issues early.

🔄 Status Update

This issue has become less relevant due to architectural changes. The application now uses built-in models instead of external model files, which significantly reduces the need for file-based validation.

✅ Current Implementation

• ✅ Built-in model validation (ResNet18 compiled into binary)
• ✅ Model loading error handling with fallback to dummy models
• ✅ Input/output dimension validation during inference
• ✅ Clear error messages for model loading failures
• ✅ Automatic model availability checking

🔄 Remaining Relevant Items

• Add --skip-validation flag for advanced users
• Enhanced startup validation for built-in models
• Test inference validation during startup

Implementation Notes

Since models are now built-in:

• No file existence/readability checks needed
• Model format validation happens at compile time
• Input/output dimensions are statically defined
• Test inference could still be valuable for startup validation

Estimated Difficulty

Beginner - 1-2 hours (reduced scope due to built-in models)