Add cp command to copy files out of containers, binary-safe

`portainer-cli cp <stack> <container>:<path> <dest>` goes through Docker's
archive API, so unlike `console --run "cat …"` there's no TTY in between and
binary files (database dumps) arrive intact. Works like `docker cp` for files
and directories; a dest of "-" writes a single file to stdout.

Stack and container lookup moves from Console into a shared Resolver module.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/portainer_cli.rb

@@ -9,6 +9,7 @@ require_relative 'portainer_cli/commands/list'
 require_relative 'portainer_cli/commands/create'
 require_relative 'portainer_cli/commands/exec'
 require_relative 'portainer_cli/commands/console'
+require_relative 'portainer_cli/commands/cp'
 
 module PortainerCli
   module CLI
@@ -34,6 +35,9 @@ module PortainerCli
           --endpoint ID                                          Disambiguate when stack name exists on multiple endpoints
           --shell SHELL                                          Shell to use (default: /bin/sh)
           --run CMD                                              Run command instead of a bare shell
+        portainer-cli cp <stack> <container>:<path> <dest>      Copy a file/directory out of a container (binary-safe)
+          --endpoint ID                                          Disambiguate when stack name exists on multiple endpoints
+          --quiet                                                Suppress status output; <dest> of - writes to stdout
         portainer-cli exec <endpoint-id> <container>            Open interactive shell (manual endpoint)
           --shell SHELL                                          Shell to use (default: /bin/sh)
 
@@ -60,6 +64,10 @@ module PortainerCli
         require_config!(config)
         client = Client.new(config)
         Commands::Console.new(config, client, debug: debug).run(argv)
+      when 'cp'
+        require_config!(config)
+        client = Client.new(config)
+        Commands::Cp.new(config, client).run(argv)
       when 'exec', 'shell'
         require_config!(config)
         client = Client.new(config)