Model capabilities 734 (#842)

internal/config,server: implement model capabilities

- define the capabilities of a model using a simple config block on the
model
- v1/models renders out capabilities to be compatible with openrouter,
huggingface chat, and mistral formats for broader compatibility
- add support for capabilities in UI

Fixes #734

internal/config/config.go

@@ -447,6 +447,10 @@ func LoadConfigFromReader(r io.Reader) (Config, error) {
 			}
 		}
 
+		if err = modelConfig.Capabilities.Validate(); err != nil {
+			return Config{}, fmt.Errorf("model %s: %w", modelId, err)
+		}
+
 		// Validate SetParamsByID keys and values
 		for key, paramMap := range modelConfig.Filters.SetParamsByID {
 			if matches := macroPatternRegex.FindAllStringSubmatch(key, -1); len(matches) > 0 {