feat(claude): add model alias mapping and improve key normalization

- Introduced model alias mapping for Claude configurations, enabling upstream and client-facing model name associations.
- Added `computeClaudeModelsHash` to generate a consistent hash for model aliases.
- Implemented `normalizeClaudeKey` function to standardize input API key configuration, including models.
- Enhanced executor to resolve model aliases to upstream names dynamically.
- Updated documentation and configuration examples to reflect new model alias support.

internal/config/config.go

@@ -94,6 +94,18 @@ type ClaudeKey struct {
 
 	// ProxyURL overrides the global proxy setting for this API key if provided.
 	ProxyURL string `yaml:"proxy-url" json:"proxy-url"`
+
+	// Models defines upstream model names and aliases for request routing.
+	Models []ClaudeModel `yaml:"models" json:"models"`
+}
+
+// ClaudeModel describes a mapping between an alias and the actual upstream model name.
+type ClaudeModel struct {
+	// Name is the upstream model identifier used when issuing requests.
+	Name string `yaml:"name" json:"name"`
+
+	// Alias is the client-facing model name that maps to Name.
+	Alias string `yaml:"alias" json:"alias"`
 }
 
 // CodexKey represents the configuration for a Codex API key,