fix(labels): improve delete command and fix --id flag type (#865)

## Summary

Fix the `tea labels delete` and `tea labels update` commands which were silently ignoring the `--id` flag.

## Problem

Both commands used `IntFlag` for the `--id` parameter but called `ctx.Int64("id")` to retrieve the value. This type mismatch caused the ID to always be read as `0`, making the commands useless.

**Before (bug):**
```bash
$ tea labels delete --id 36 --debug
DELETE: .../labels/0   # Wrong! ID ignored
```

**After (fix):**
```bash
$ tea labels delete --id 36 --debug
GET: .../labels/36     # Verify exists
DELETE: .../labels/36  # Correct ID
Label 'my-label' (id: 36) deleted successfully
```

## Changes

### labels/delete.go
- Change `IntFlag` to `Int64Flag` to match `ctx.Int64()` usage
- Make `--id` flag required
- Verify label exists before attempting deletion
- Provide clear error messages with label name and ID context
- Print success message after deletion

### labels/update.go
- Change `IntFlag` to `Int64Flag` to fix the same bug

## Test plan

- [x] `go test ./...` passes
- [x] `go vet ./...` passes
- [x] `gofmt` check passes
- [x] Manual testing confirms ID is now correctly passed to API
- [ ] CI passes

Reviewed-on: https://gitea.com/gitea/tea/pulls/865
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Alain Thiffault <athiffau@effectivemomentum.com>
Co-committed-by: Alain Thiffault <athiffau@effectivemomentum.com>

cmd/labels/delete.go

@@ -5,6 +5,7 @@ package labels
 
 import (
 	stdctx "context"
+	"fmt"
 
 	"code.gitea.io/tea/cmd/flags"
 	"code.gitea.io/tea/modules/context"
@@ -21,9 +22,10 @@ var CmdLabelDelete = cli.Command{
 	ArgsUsage:   " ", // command does not accept arguments
 	Action:      runLabelDelete,
 	Flags: append([]cli.Flag{
-		&cli.IntFlag{
-			Name:  "id",
-			Usage: "label id",
+		&cli.Int64Flag{
+			Name:     "id",
+			Usage:    "label id",
+			Required: true,
 		},
 	}, flags.AllDefaultFlags...),
 }
@@ -32,6 +34,20 @@ func runLabelDelete(_ stdctx.Context, cmd *cli.Command) error {
 	ctx := context.InitCommand(cmd)
 	ctx.Ensure(context.CtxRequirement{RemoteRepo: true})
 
-	_, err := ctx.Login.Client().DeleteLabel(ctx.Owner, ctx.Repo, ctx.Int64("id"))
-	return err
+	labelID := ctx.Int64("id")
+	client := ctx.Login.Client()
+
+	// Verify the label exists first
+	label, _, err := client.GetRepoLabel(ctx.Owner, ctx.Repo, labelID)
+	if err != nil {
+		return fmt.Errorf("failed to get label %d: %w", labelID, err)
+	}
+
+	_, err = client.DeleteLabel(ctx.Owner, ctx.Repo, labelID)
+	if err != nil {
+		return fmt.Errorf("failed to delete label '%s' (id: %d): %w", label.Name, labelID, err)
+	}
+
+	fmt.Printf("Label '%s' (id: %d) deleted successfully\n", label.Name, labelID)
+	return nil
 }