Add rails-stats command line executable

Add a standalone `rails-stats` executable so the tool can be run against a
directory without setting up a Rakefile. It accepts both absolute and relative
paths, defaults to the current directory when none is given, and optionally
takes a `json` second argument for JSON output.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: etagwerker

CHANGELOG.md

@@ -1,5 +1,6 @@
 # main ([unreleased](https://github.com/fastruby/rails_stats/compare/v2.1.0...main))
 
+* [FEATURE: Add a `rails-stats` command line executable that accepts an absolute or relative directory](https://github.com/fastruby/rails_stats/pull/49)
 * [FEATURE: Support component-based and Packwerk (packs) applications with a per-pack and Core breakdown](https://github.com/fastruby/rails_stats/issues/23)
 * [BUGFIX: Respect an explicit path argument (e.g. `rake stats[packs/pack1]`) when running inside a booted Rails app](https://github.com/fastruby/rails_stats/issues/23)
 * [CHORE: Improve the GH Test Workflow](https://github.com/fastruby/rails_stats/pull/35)

README.md

@@ -6,6 +6,29 @@ There were a few things missing to the included `rake stats`
 
 RailsStats mainly adds the ability to be run from outside the project in question. This can be helpful if the app you are interested in can not be booted for some reason.
 
+### Run it as a command line tool
+
+Once the gem is installed you can point the `rails-stats` executable at any
+directory, without setting up a `Rakefile`. It accepts both absolute and
+relative paths:
+
+```bash
+$ rails-stats /path/to/app
+$ rails-stats path/to/app
+```
+
+When no path is given it defaults to the current directory:
+
+```bash
+$ rails-stats
+```
+
+You can also request JSON output by passing `json` as a second argument:
+
+```bash
+$ rails-stats path/to/app json
+```
+
 ### Run it outside Rails project
 
 You will need a `Rakefile` in the directory where you call `rake` and you will

bin/rails-stats

@@ -0,0 +1,27 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+# Standalone CLI for running rails_stats against a directory without having to
+# set up a Rakefile. Accepts both absolute and relative paths:
+#
+#   rails-stats /path/to/app
+#   rails-stats path/to/app
+#   rails-stats                 # defaults to the current directory
+#   rails-stats path/to/app json
+#
+$LOAD_PATH.unshift(File.expand_path("../lib", __dir__))
+
+require "rails_stats/all"
+
+path = ARGV[0] || "."
+format = ARGV[1] || ""
+
+root_directory = File.absolute_path(path)
+
+unless File.directory?(root_directory)
+  warn "rails-stats: no such directory - #{path}"
+  exit 1
+end
+
+puts "\nDirectory: #{root_directory}\n\n"
+RailsStats::CodeStatistics.new(root_directory, format: format).to_s