fix: restore hints when unauthorized (#321)

## Summary
Restores helpful hints that were lost in the error handling refactor
(#279):
- Added hint for `ErrUnauthorized`: "Did you run `dbc auth login`?"
- Restored simpler hint for `ErrUnauthorizedColumnar` with original
wording from #255

## Context
These hints were originally added in #255 to help users troubleshoot
authorization issues when installing private drivers. During the error
handling refactor in #279, these hints were either removed or changed to
more verbose messages.

## Changes
- `cmd/dbc/main.go`: Updated `formatErr()` function to include both
helpful hints

Fixes #315

---------

Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>
Co-authored-by: zeroshade <555095+zeroshade@users.noreply.github.com>

Author: zeroshade

cmd/dbc/main.go

@@ -153,7 +153,8 @@ func formatErr(err error) string {
 	case errors.Is(err, auth.ErrNoTrialLicense):
 		return errStyle.Render("Could not download license, trial not started")
 	case errors.Is(err, dbc.ErrUnauthorized):
-		return errStyle.Render(err.Error())
+		return errStyle.Render(err.Error()) + "\n" +
+			msgStyle.Render("Did you run `dbc auth login`?")
 	case errors.Is(err, dbc.ErrUnauthorizedColumnar):
 		return errStyle.Render(err.Error()) + "\n" +
 			msgStyle.Render("Installing this driver requires a license. Verify you have an active license at https://console.columnar.tech/licenses and try this command again. Contact support@columnar.tech if you believe this is an error.")

cmd/dbc/main_test.go

@@ -17,13 +17,55 @@ package main
 import (
 	"bytes"
 	"context"
+	"fmt"
+	"strings"
 	"testing"
 	"time"
 
 	tea "github.com/charmbracelet/bubbletea"
+	"github.com/columnar-tech/dbc"
 	"github.com/stretchr/testify/require"
 )
 
+func TestFormatErr(t *testing.T) {
+	tests := []struct {
+		name          string
+		err           error
+		wantSubstring []string
+	}{
+		{
+			name:          "ErrUnauthorized direct",
+			err:           dbc.ErrUnauthorized,
+			wantSubstring: []string{dbc.ErrUnauthorized.Error(), "Did you run `dbc auth login`?"},
+		},
+		{
+			name:          "ErrUnauthorized wrapped",
+			err:           fmt.Errorf("operation failed: %w", dbc.ErrUnauthorized),
+			wantSubstring: []string{dbc.ErrUnauthorized.Error(), "Did you run `dbc auth login`?"},
+		},
+		{
+			name:          "ErrUnauthorizedColumnar direct",
+			err:           dbc.ErrUnauthorizedColumnar,
+			wantSubstring: []string{dbc.ErrUnauthorizedColumnar.Error(), "active license", "support@columnar.tech"},
+		},
+		{
+			name:          "ErrUnauthorizedColumnar wrapped",
+			err:           fmt.Errorf("operation failed: %w", dbc.ErrUnauthorizedColumnar),
+			wantSubstring: []string{dbc.ErrUnauthorizedColumnar.Error(), "active license", "support@columnar.tech"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := formatErr(tt.err)
+			for _, want := range tt.wantSubstring {
+				require.True(t, strings.Contains(got, want),
+					"formatErr(%v) = %q, expected to contain %q", tt.err, got, want)
+			}
+		})
+	}
+}
+
 func TestCmdStatus(t *testing.T) {
 	tests := []struct {
 		name   string