refactor: improve config validation

This commit refactors the configuration validation logic in the `initConfig` function.

Previously, the validation for `short_model` and `long_model` was done within the `rootCmd.Run` function, which meant that errors would only be surfaced when the diff command was actually executed.

This change moves the validation to the `initConfig` function, ensuring that configuration errors related to empty `short_model` or `long_model`, or a negative `threshold`, are caught earlier during the initialization phase. This provides a better user experience by surfacing configuration issues immediately upon command execution, rather than during the processing of diffs.

Additionally, it simplifies the logic by removing redundant checks within the `rootCmd.Run` function. The validation for `short_model` and `long_model` is now handled solely in `initConfig`, and the `threshold` validation is also added there.
---
{"auto-commit-msg":{"language":"rust","version":"0.4.0-dev","model":"gemini-2.5-flash-lite","response_time":2.11,"execution_time":2.15}}

Author: sestrella

cmd/root.go

@@ -97,15 +97,9 @@ var rootCmd = &cobra.Command{
 		var model string
 		if totalChanges < totalChangesThreshold {
 			model = config.Diff.ShortModel
-			if model == "" {
-				return errors.New("short_model cannot be empty")
-			}
 			log.Printf("git diff total changes %d under %d threshold, using model for short diffs: %s\n", totalChanges, totalChangesThreshold, model)
 		} else {
 			model = config.Diff.LongModel
-			if model == "" {
-				return errors.New("long_model cannot be empty")
-			}
 			log.Printf("git diff total changes %d over %d threshold, using model for long diffs: %s\n", totalChanges, totalChangesThreshold, model)
 		}
 		if config.Provider.ApiKey == "" {
@@ -229,4 +223,19 @@ func initConfig() {
 	if err := viper.Unmarshal(&config); err != nil {
 		cobra.CheckErr(err)
 	}
+
+	shortModel := config.Diff.ShortModel
+	if shortModel == "" {
+		cobra.CheckErr("diff.short_model cannot be empty")
+	}
+
+	longModel := config.Diff.LongModel
+	if longModel == "" {
+		cobra.CheckErr("diff.long_model cannot be empty")
+	}
+
+	threshold := config.Diff.Threshold
+	if threshold < 0 {
+		cobra.CheckErr("diff.threshold should be greater than 0")
+	}
 }