feat: add actions management commands (#796)

## Summary

This PR adds comprehensive Actions secrets and variables management functionality to the tea CLI, enabling users to manage their repository's CI/CD configuration directly from the command line.

## Features Added

### Actions Secrets Management
- **List secrets**: `tea actions secrets list` - Display all repository action secrets
- **Create secrets**: `tea actions secrets create <name>` - Create new secrets with interactive prompts
- **Delete secrets**: `tea actions secrets delete <name>` - Remove existing secrets

### Actions Variables Management
- **List variables**: `tea actions variables list` - Display all repository action variables
- **Set variables**: `tea actions variables set <name> <value>` - Create or update variables
- **Delete variables**: `tea actions variables delete <name>` - Remove existing variables

## Implementation Details

- **Interactive prompts**: Secure input handling for sensitive secret values
- **Input validation**: Proper validation for secret/variable names and values
- **Table formatting**: Consistent output formatting with existing tea commands
- **Error handling**: Comprehensive error handling and user feedback
- **Test coverage**: Full test suite for all functionality

## Usage Examples

```bash
# Secrets management
tea actions secrets list
tea actions secrets create API_KEY    # Will prompt securely for value
tea actions secrets delete OLD_SECRET

# Variables management
tea actions variables list
tea actions variables set API_URL https://api.example.com
tea actions variables delete UNUSED_VAR
```

## Related Issue

Resolves #797

## Testing

- All new functionality includes comprehensive unit tests
- Integration with existing tea CLI patterns and conventions
- Validated against Gitea Actions API

Reviewed-on: https://gitea.com/gitea/tea/pulls/796
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Ross Golder <ross@golder.org>
Co-committed-by: Ross Golder <ross@golder.org>

cmd/actions/variables/delete_test.go

@@ -0,0 +1,98 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package variables
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestVariablesDeleteValidation(t *testing.T) {
+	tests := []struct {
+		name    string
+		args    []string
+		wantErr bool
+	}{
+		{
+			name:    "valid variable name",
+			args:    []string{"VALID_VARIABLE"},
+			wantErr: false,
+		},
+		{
+			name:    "valid lowercase name",
+			args:    []string{"valid_variable"},
+			wantErr: false,
+		},
+		{
+			name:    "no args",
+			args:    []string{},
+			wantErr: true,
+		},
+		{
+			name:    "too many args",
+			args:    []string{"VARIABLE1", "VARIABLE2"},
+			wantErr: true,
+		},
+		{
+			name:    "invalid variable name",
+			args:    []string{"invalid-variable"},
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := validateVariableDeleteArgs(tt.args)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("validateVariableDeleteArgs() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestVariablesDeleteFlags(t *testing.T) {
+	cmd := CmdVariablesDelete
+
+	// Test command properties
+	if cmd.Name != "delete" {
+		t.Errorf("Expected command name 'delete', got %s", cmd.Name)
+	}
+
+	// Check that rm is one of the aliases
+	hasRmAlias := false
+	for _, alias := range cmd.Aliases {
+		if alias == "rm" {
+			hasRmAlias = true
+			break
+		}
+	}
+	if !hasRmAlias {
+		t.Error("Expected 'rm' to be one of the aliases for delete command")
+	}
+
+	if cmd.ArgsUsage != "<variable-name>" {
+		t.Errorf("Expected ArgsUsage '<variable-name>', got %s", cmd.ArgsUsage)
+	}
+
+	if cmd.Usage == "" {
+		t.Error("Delete command should have usage text")
+	}
+
+	if cmd.Description == "" {
+		t.Error("Delete command should have description")
+	}
+}
+
+// validateVariableDeleteArgs validates arguments for the delete command
+func validateVariableDeleteArgs(args []string) error {
+	if len(args) == 0 {
+		return fmt.Errorf("variable name is required")
+	}
+
+	if len(args) > 1 {
+		return fmt.Errorf("only one variable name allowed")
+	}
+
+	return validateVariableName(args[0])
+}