Add sample .env file for environment configuration

- Created .env.example with all required environment variables
- Updated .gitignore to exclude .env files from version control
- Includes instructions for generating secure SECRET_KEY_BASE

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.env.example

@@ -0,0 +1,14 @@
+# Database Configuration
+POSTGRES_USER=postgres
+POSTGRES_PASSWORD=postgres
+POSTGRES_DB=my_first_elixir_vibe_code_dev
+
+# Phoenix Configuration
+DATABASE_URL=ecto://postgres:postgres@db/my_first_elixir_vibe_code_dev
+SECRET_KEY_BASE=PNosxXTGA8DhjwcE5QWJkJZr400AFXjIWu27dEFQg/QJE3RyCna6HePec1Sjgz6W
+PHX_HOST=localhost
+PORT=4000
+
+# Important: For production, generate a new SECRET_KEY_BASE with:
+# docker-compose run --rm web bin/my_first_elixir_vibe_code eval "IO.puts(:crypto.strong_rand_bytes(64) |> Base.encode64())"
+# or locally with: mix phx.gen.secret

.gitignore

@@ -35,3 +35,6 @@ my_first_elixir_vibe_code-*.tar
 npm-debug.log
 /assets/node_modules/
 
+# Environment variables
+.env
+