Refactor help system to consolidate error messages and command-specific help

- Simplify main help to show brief command descriptions only
- Add --help support to all commands with detailed usage information
- Replace duplicated help text in error messages with error + help pattern
- Remove 'help' command in favor of consistent --help flag usage
- Add helper functions CheckForHelpFlag() and ShowErrorWithHelp() for standardization
- Refactor deploy command to reduce cognitive complexity and improve maintainability

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

enable.go

@@ -8,6 +8,27 @@ import (
 )
 
 func RunEnableCommand(args []string, pluginPath string) error {
+	helpText := `Enable plugin in Mattermost server
+
+Usage:
+  pluginctl enable [options]
+
+Options:
+  --help, -h    Show this help message
+
+Description:
+  Enables the plugin in the connected Mattermost server. The plugin must already
+  be uploaded to the server for this command to work.
+
+Examples:
+  pluginctl enable                            # Enable plugin from current directory
+  pluginctl --plugin-path /path/to/plugin enable # Enable plugin at specific path`
+
+	// Check for help flag
+	if CheckForHelpFlag(args, helpText) {
+		return nil
+	}
+
 	return runPluginCommand(args, pluginPath, enablePlugin)
 }