fix: validate domain search query includes TLD (#220)

* fix: validate domain search query includes TLD

When searching without a TLD (e.g., `zeabur domain search antnest`),
the API returns `{"available": false, "tld": ""}` which is misleading.
Users may think the domain is taken when it was just an invalid query.

Add validation to require a dot in the domain name and show a helpful
error message guiding users to provide a full domain with TLD.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* refactor: use ContainsRune for single character

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Yi-Jyun Pan <pan93412@gmail.com>

Author: 3 people

internal/cmd/domain/search/search.go

@@ -3,6 +3,7 @@ package search
 import (
 	"context"
 	"fmt"
+	"strings"
 
 	"github.com/briandowns/spinner"
 	"github.com/spf13/cobra"
@@ -43,6 +44,10 @@ func runSearch(f *cmdutil.Factory, opts *Options) error {
 		opts.query = query
 	}
 
+	if !strings.ContainsRune(opts.query, '.') {
+		return fmt.Errorf("please provide a full domain name with TLD (e.g., example.com, example.io)")
+	}
+
 	s := spinner.New(cmdutil.SpinnerCharSet, cmdutil.SpinnerInterval,
 		spinner.WithColor(cmdutil.SpinnerColor),
 		spinner.WithSuffix(" Checking availability..."),