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

db/seeds.rb

@@ -0,0 +1,9 @@
+# This file should ensure the existence of records required to run the application in every environment (production,
+# development, test). The code here should be idempotent so that it can be executed at any point in every environment.
+# The data can then be loaded with the bin/rails db:seed command (or created alongside the database with db:setup).
+#
+# Example:
+#
+#   ["Action", "Comedy", "Drama", "Horror"].each do |genre_name|
+#     MovieGenre.find_or_create_by!(name: genre_name)
+#   end