Set up Rails 8 application foundation

- Generate Rails 8.1 app with PostgreSQL and TailwindCSS
- Add docker-compose.yml (postgres:17) for local database
- Configure database.yml to connect to Dockerized Postgres via env vars
- Add Pages#home root route, application layout, and navbar partial

config/boot.rb

@@ -0,0 +1,4 @@
+ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../Gemfile", __dir__)
+
+require "bundler/setup" # Set up gems listed in the Gemfile.
+require "bootsnap/setup" # Speed up boot time by caching expensive operations.