-y/--yes flag for non-interactive mode (fixes #46)

Also makes Modrinth auto-accept search results with only 1 result, to be
consistent with CurseForge.

cmdshared/prompt.go

@@ -0,0 +1,28 @@
+package cmdshared
+
+import (
+	"bufio"
+	"fmt"
+	"github.com/spf13/viper"
+	"os"
+	"strings"
+)
+
+func PromptYesNo(prompt string) bool {
+	fmt.Print(prompt)
+	if viper.GetBool("non-interactive") {
+		fmt.Println("Y (non-interactive mode)")
+		return true
+	}
+	answer, err := bufio.NewReader(os.Stdin).ReadString('\n')
+	if err != nil {
+		fmt.Printf("Failed to prompt user: %v\n", err)
+		os.Exit(1)
+	}
+
+	ansNormal := strings.ToLower(strings.TrimSpace(answer))
+	if len(ansNormal) > 0 && ansNormal[0] == 'n' {
+		return false
+	}
+	return true
+}