Initial implementation of portainer-cli

Ruby CLI tool for interacting with the Portainer API. Supports listing
endpoints/stacks/containers/volumes/networks, creating stacks and containers,
and opening an interactive exec session in a container via WebSocket.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/portainer_cli/commands/base.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+module PortainerCli
+  module Commands
+    module Base
+      RESET  = "\e[0m"
+      BOLD   = "\e[1m"
+      CYAN   = "\e[36m"
+      GREEN  = "\e[32m"
+      YELLOW = "\e[33m"
+      RED    = "\e[31m"
+      DIM    = "\e[2m"
+
+      def colorize?
+        $stdout.tty?
+      end
+
+      def bold(str)    = colorize? ? "#{BOLD}#{str}#{RESET}"   : str
+      def cyan(str)    = colorize? ? "#{CYAN}#{str}#{RESET}"   : str
+      def green(str)   = colorize? ? "#{GREEN}#{str}#{RESET}"  : str
+      def yellow(str)  = colorize? ? "#{YELLOW}#{str}#{RESET}" : str
+      def red(str)     = colorize? ? "#{RED}#{str}#{RESET}"    : str
+      def dim(str)     = colorize? ? "#{DIM}#{str}#{RESET}"    : str
+
+      def print_table(headers, rows)
+        widths = headers.each_with_index.map do |h, i|
+          [h.length, rows.map { |r| r[i].to_s.length }.max || 0].max
+        end
+
+        sep = widths.map { |w| '-' * (w + 2) }.join('+')
+        header_row = headers.each_with_index.map { |h, i| " #{bold(h.ljust(widths[i]))} " }.join('|')
+
+        puts sep
+        puts header_row
+        puts sep
+        rows.each do |row|
+          puts row.each_with_index.map { |cell, i| " #{cell.to_s.ljust(widths[i])} " }.join('|')
+        end
+        puts sep
+      end
+
+      def error(msg)
+        $stderr.puts red("Error: #{msg}")
+        exit 1
+      end
+
+      def require_config!(config)
+        error("Not configured. Run: portainer-cli configure") unless config.valid?
+      end
+    end
+  end
+end