Read database, host and SMTP settings from a .env file

- gem dotenv loads .env (and .env.<environment>[.local]) at startup; real
  environment variables take precedence.
- database.yml takes host, port, user, password and name from
  NUMOLUS_DATABASE_*; the database is called numolus by default.
- .env.example documents every setting; .env itself stays ignored.

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

.env.example

@@ -0,0 +1,26 @@
+# numolus settings -- copy to .env (same directory) and fill in.
+# .env is read at startup (gem dotenv) and never committed. Variables that
+# are already set in the real environment take precedence over this file.
+# Environment-specific files are read too: .env.production, .env.development
+# (and *.local variants).
+
+# ---- Database (PostgreSQL) --------------------------------------------------
+# Unset host/user/password = local socket as the current OS user (development).
+NUMOLUS_DATABASE_NAME=numolus
+NUMOLUS_DATABASE_HOST=localhost
+NUMOLUS_DATABASE_PORT=5432
+NUMOLUS_DATABASE_USER=numolus
+NUMOLUS_DATABASE_PASSWORD=
+
+# ---- Server -------------------------------------------------------------------
+# Host name used in links in mails (sign-in, invitations)
+NUMOLUS_HOST=numolus.wicom.li
+# Rails secret (production): generate with  bin/rails secret
+SECRET_KEY_BASE=
+
+# ---- Mail (production; development shows mails at /letter_opener) ------------
+NUMOLUS_MAIL_FROM="numolus <noreply@wicom.li>"
+SMTP_ADDRESS=smtp.example.com
+SMTP_PORT=587
+SMTP_USER_NAME=
+SMTP_PASSWORD=

.gitignore

@@ -26,4 +26,5 @@ node_modules
 !/storage/.keep
 /config/master.key
 /.env*
+!/.env.example
 /vendor/gems

Gemfile

@@ -37,6 +37,10 @@ group :development do
   gem "web-console"
 end
 
+# Settings and secrets (database, SMTP, host) from a .env file in the project
+# directory; real environment variables win -- see .env.example
+gem "dotenv"
+
 # Vite as the frontend build, integrated into Rails [https://vite-ruby.netlify.app]
 gem "vite_rails"
 

Gemfile.lock

@@ -97,6 +97,7 @@ GEM
     debug (1.11.1)
       irb (~> 1.10)
       reline (>= 0.3.8)
+    dotenv (3.2.0)
     drb (2.2.3)
     dry-cli (1.4.1)
     erb (6.0.7)
@@ -300,6 +301,7 @@ DEPENDENCIES
   brakeman
   bundler-audit
   debug
+  dotenv
   letter_opener_web
   pg (~> 1.1)
   puma (>= 5.0)

README.md

@@ -28,11 +28,12 @@ kommen über ActionCable sofort bei den anderen an (Yjs, siehe
 [`app/frontend/collab/`](app/frontend/collab/)), jede Person hat ihr eigenes
 Undo, und die Auswahl der anderen ist als farbiger Rahmen zu sehen. Details: [`docs/konzept-teilen-und-zusammenarbeit.md`](docs/konzept-teilen-und-zusammenarbeit.md).
 
-Mails landen in der Entwicklung nicht im Postfach, sondern unter
-<http://localhost:3000/letter_opener>. Produktion braucht `SMTP_ADDRESS`,
-`SMTP_USER_NAME`, `SMTP_PASSWORD`, `NUMOLUS_MAIL_FROM`, `NUMOLUS_HOST` und
-`NUMOLUS_DATABASE_PASSWORD`; Solid Queue, Cache und Cable liegen in derselben
-Datenbank wie die Daten.
+**Konfiguration:** Datenbank-Zugang, Server-Name, SMTP und `SECRET_KEY_BASE`
+stehen in einer `.env` im Projektverzeichnis – Vorlage kopieren und ausfüllen:
+`cp .env.example .env`. Die Datei wird nie committet; echte
+Umgebungsvariablen haben Vorrang. Solid Queue, Cache und Cable liegen in
+derselben Datenbank wie die Daten. Mails landen in der Entwicklung nicht im
+Postfach, sondern unter <http://localhost:3000/letter_opener>.
 
 ---
 

config/database.yml

@@ -15,14 +15,17 @@
 default: &default
   adapter: postgresql
   encoding: unicode
-  # For details on connection pooling, see Rails configuration guide
-  # https://guides.rubyonrails.org/configuring.html#database-pooling
   max_connections: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
-
+  # Connection details come from the environment, usually a .env file in
+  # the project directory (see .env.example). Unset = local socket, own user.
+  host: <%= ENV["NUMOLUS_DATABASE_HOST"] %>
+  port: <%= ENV["NUMOLUS_DATABASE_PORT"] %>
+  username: <%= ENV["NUMOLUS_DATABASE_USER"] %>
+  password: <%= ENV["NUMOLUS_DATABASE_PASSWORD"] %>
 
 development:
   <<: *default
-  database: numolus_development
+  database: <%= ENV.fetch("NUMOLUS_DATABASE_NAME", "numolus") %>
 
   # The specified database role being used to connect to PostgreSQL.
   # To create additional roles in PostgreSQL see `$ createuser --help`.
@@ -59,9 +62,8 @@ test:
   database: numolus_test
 
 # Production: one database for everything -- app data, Solid Queue, Solid
-# Cache and Solid Cable. The password comes from NUMOLUS_DATABASE_PASSWORD.
+# Cache and Solid Cable. Credentials via NUMOLUS_DATABASE_* (see .env.example).
 production:
   <<: *default
-  database: numolus_production
-  username: numolus
-  password: <%= ENV["NUMOLUS_DATABASE_PASSWORD"] %>
+  database: <%= ENV.fetch("NUMOLUS_DATABASE_NAME", "numolus") %>
+  username: <%= ENV.fetch("NUMOLUS_DATABASE_USER", "numolus") %>