feat: regex support for model-mappings

internal/config/config.go

@@ -144,6 +144,11 @@ type AmpModelMapping struct {
 	// To is the target model name to route to (e.g., "claude-sonnet-4").
 	// The target model must have available providers in the registry.
 	To string `yaml:"to" json:"to"`
+
+    // Regex indicates whether the 'from' field should be interpreted as a regular
+    // expression for matching model names. When true, this mapping is evaluated
+    // after exact matches and in the order provided. Defaults to false (exact match).
+    Regex bool `yaml:"regex,omitempty" json:"regex,omitempty"`
 }
 
 // AmpCode groups Amp CLI integration settings including upstream routing,