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/set_test.go

@@ -0,0 +1,213 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package variables
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestValidateVariableName(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   string
+		wantErr bool
+	}{
+		{
+			name:    "valid name",
+			input:   "VALID_VARIABLE_NAME",
+			wantErr: false,
+		},
+		{
+			name:    "valid name with numbers",
+			input:   "VARIABLE_123",
+			wantErr: false,
+		},
+		{
+			name:    "valid lowercase",
+			input:   "valid_variable",
+			wantErr: false,
+		},
+		{
+			name:    "valid mixed case",
+			input:   "Mixed_Case_Variable",
+			wantErr: false,
+		},
+		{
+			name:    "invalid - spaces",
+			input:   "INVALID VARIABLE",
+			wantErr: true,
+		},
+		{
+			name:    "invalid - special chars",
+			input:   "INVALID-VARIABLE!",
+			wantErr: true,
+		},
+		{
+			name:    "invalid - starts with number",
+			input:   "1INVALID",
+			wantErr: true,
+		},
+		{
+			name:    "invalid - empty",
+			input:   "",
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := validateVariableName(tt.input)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("validateVariableName(%q) error = %v, wantErr %v", tt.input, err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestGetVariableSourceArgs(t *testing.T) {
+	tests := []struct {
+		name    string
+		args    []string
+		wantErr bool
+	}{
+		{
+			name:    "valid args",
+			args:    []string{"VALID_VARIABLE", "variable_value"},
+			wantErr: false,
+		},
+		{
+			name:    "valid lowercase",
+			args:    []string{"valid_variable", "value"},
+			wantErr: false,
+		},
+		{
+			name:    "missing name",
+			args:    []string{},
+			wantErr: true,
+		},
+		{
+			name:    "too many args",
+			args:    []string{"VARIABLE_NAME", "value", "extra"},
+			wantErr: true,
+		},
+		{
+			name:    "invalid variable name",
+			args:    []string{"invalid-variable", "value"},
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Test argument validation only
+			if len(tt.args) == 0 {
+				if !tt.wantErr {
+					t.Error("Expected error for empty args")
+				}
+				return
+			}
+
+			if len(tt.args) > 2 {
+				if !tt.wantErr {
+					t.Error("Expected error for too many args")
+				}
+				return
+			}
+
+			// Test variable name validation
+			err := validateVariableName(tt.args[0])
+			if (err != nil) != tt.wantErr {
+				t.Errorf("validateVariableName() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestVariableNameValidation(t *testing.T) {
+	// Test that variable names follow GitHub Actions/Gitea Actions conventions
+	validNames := []string{
+		"VALID_VARIABLE",
+		"API_URL",
+		"DATABASE_HOST",
+		"VARIABLE_123",
+		"mixed_Case_Variable",
+		"lowercase_variable",
+		"UPPERCASE_VARIABLE",
+	}
+
+	invalidNames := []string{
+		"Invalid-Dashes",
+		"INVALID SPACES",
+		"123_STARTS_WITH_NUMBER",
+		"",           // Empty
+		"INVALID!@#", // Special chars
+	}
+
+	for _, name := range validNames {
+		t.Run("valid_"+name, func(t *testing.T) {
+			err := validateVariableName(name)
+			if err != nil {
+				t.Errorf("validateVariableName(%q) should be valid, got error: %v", name, err)
+			}
+		})
+	}
+
+	for _, name := range invalidNames {
+		t.Run("invalid_"+name, func(t *testing.T) {
+			err := validateVariableName(name)
+			if err == nil {
+				t.Errorf("validateVariableName(%q) should be invalid, got no error", name)
+			}
+		})
+	}
+}
+
+func TestVariableValueValidation(t *testing.T) {
+	tests := []struct {
+		name    string
+		value   string
+		wantErr bool
+	}{
+		{
+			name:    "valid value",
+			value:   "variable123",
+			wantErr: false,
+		},
+		{
+			name:    "valid complex value",
+			value:   "https://api.example.com/v1",
+			wantErr: false,
+		},
+		{
+			name:    "valid multiline value",
+			value:   "line1\nline2\nline3",
+			wantErr: false,
+		},
+		{
+			name:    "empty value allowed",
+			value:   "",
+			wantErr: false, // Variables can be empty unlike secrets
+		},
+		{
+			name:    "whitespace only allowed",
+			value:   "   \t\n   ",
+			wantErr: false, // Variables can contain whitespace
+		},
+		{
+			name:    "very long value",
+			value:   strings.Repeat("a", 65537), // Over 64KB
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := validateVariableValue(tt.value)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("validateVariableValue() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}