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.go

@@ -0,0 +1,117 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package variables
+
+import (
+	stdctx "context"
+	"fmt"
+	"io"
+	"os"
+	"regexp"
+	"strings"
+
+	"code.gitea.io/tea/cmd/flags"
+	"code.gitea.io/tea/modules/context"
+
+	"github.com/urfave/cli/v3"
+)
+
+// CmdVariablesSet represents a sub command to set action variables
+var CmdVariablesSet = cli.Command{
+	Name:        "set",
+	Aliases:     []string{"create", "update"},
+	Usage:       "Set an action variable",
+	Description: "Set a variable for use in repository actions and workflows",
+	ArgsUsage:   "<variable-name> [variable-value]",
+	Action:      runVariablesSet,
+	Flags: append([]cli.Flag{
+		&cli.StringFlag{
+			Name:  "file",
+			Usage: "read variable value from file",
+		},
+		&cli.BoolFlag{
+			Name:  "stdin",
+			Usage: "read variable value from stdin",
+		},
+	}, flags.AllDefaultFlags...),
+}
+
+func runVariablesSet(ctx stdctx.Context, cmd *cli.Command) error {
+	if cmd.Args().Len() == 0 {
+		return fmt.Errorf("variable name is required")
+	}
+
+	c := context.InitCommand(cmd)
+	client := c.Login.Client()
+
+	variableName := cmd.Args().First()
+	var variableValue string
+
+	// Determine how to get the variable value
+	if cmd.String("file") != "" {
+		// Read from file
+		content, err := os.ReadFile(cmd.String("file"))
+		if err != nil {
+			return fmt.Errorf("failed to read file: %w", err)
+		}
+		variableValue = strings.TrimSpace(string(content))
+	} else if cmd.Bool("stdin") {
+		// Read from stdin
+		content, err := io.ReadAll(os.Stdin)
+		if err != nil {
+			return fmt.Errorf("failed to read from stdin: %w", err)
+		}
+		variableValue = strings.TrimSpace(string(content))
+	} else if cmd.Args().Len() >= 2 {
+		// Use provided argument
+		variableValue = cmd.Args().Get(1)
+	} else {
+		// Interactive prompt
+		fmt.Printf("Enter variable value for '%s': ", variableName)
+		var input string
+		fmt.Scanln(&input)
+		variableValue = input
+	}
+
+	if variableValue == "" {
+		return fmt.Errorf("variable value cannot be empty")
+	}
+
+	_, err := client.CreateRepoActionVariable(c.Owner, c.Repo, variableName, variableValue)
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf("Variable '%s' set successfully\n", variableName)
+	return nil
+}
+
+// validateVariableName validates that a variable name follows the required format
+func validateVariableName(name string) error {
+	if name == "" {
+		return fmt.Errorf("variable name cannot be empty")
+	}
+
+	// Variable names can contain letters (upper/lower), numbers, and underscores
+	// Cannot start with a number
+	// Cannot contain spaces or special characters (except underscore)
+	validPattern := regexp.MustCompile(`^[A-Za-z_][A-Za-z0-9_]*$`)
+	if !validPattern.MatchString(name) {
+		return fmt.Errorf("variable name must contain only letters, numbers, and underscores, and cannot start with a number")
+	}
+
+	return nil
+}
+
+// validateVariableValue validates that a variable value is acceptable
+func validateVariableValue(value string) error {
+	// Variables can be empty or contain whitespace, unlike secrets
+
+	// Check for maximum size (64KB limit)
+	if len(value) > 65536 {
+		return fmt.Errorf("variable value cannot exceed 64KB")
+	}
+
+	return nil
+}