feat: externalize config via env vars

- Add .env.example with all configurable variables documented
  (DB URL, HTTP port/host, cookie, JWT issuer/keys, log level)
- Remove hardcoded -Dquarkus.http.host from Dockerfile ENTRYPOINT
  (application.properties already sets the default; env vars
  can now override it at runtime without conflicting with -D flags)

All env vars follow Quarkus's auto-binding convention:
property.key → PROPERTY_KEY (uppercase)

Most useful for production:
- QUARKUS_DATASOURCE_JDBC_URL: DB file path
- QUARKUS_HTTP_PORT: HTTP port
- QUARKUS_HTTP_HOST: bind interface
- APP_AUTH_COOKIE_SECURE: enable Secure flag behind HTTPS
- MP_JWT_VERIFY_PUBLICKEY_LOCATION: externalize RSA keys

.env.example

@@ -0,0 +1,49 @@
+# shot-crafter-calculator — variables de entorno
+# Las variables siguen la convencion de Quarkus: puntos → underscores, mayusculas.
+# Cualquier property de src/main/resources/application.properties se puede overridear.
+#
+# Uso:
+#   docker run --env-file .env gitea.danielarroyo.cl/proyectos/shot-crafter-calculator:latest
+#   docker run -e QUARKUS_HTTP_PORT=9090 gitea.danielarroyo.cl/proyectos/shot-crafter-calculator:latest
+
+# ===== HTTP server =====
+# QUARKUS_HTTP_PORT=8080
+# QUARKUS_HTTP_HOST=0.0.0.0
+
+# ===== Base de datos =====
+# Default: jdbc:h2:file:./data/shots (queda en /work/data/shots.mv.db dentro del container)
+# Produccion tipica (con volumen montado en /work/data):
+#   QUARKUS_DATASOURCE_JDBC_URL=jdbc:h2:file:/work/data/shots;DB_CLOSE_DELAY=-1
+# Para MySQL/Postgres cambiar tambien db-kind y credenciales:
+#   QUARKUS_DATASOURCE_DB_KIND=mysql
+#   QUARKUS_DATASOURCE_JDBC_URL=jdbc:mysql://db:3306/shots
+#   QUARKUS_DATASOURCE_USERNAME=shot
+#   QUARKUS_DATASOURCE_PASSWORD=secret
+#   QUARKUS_HIBERNATE_ORM_DATABASE_GENERATION=update
+
+# ===== JWT / Auth =====
+# MP_JWT_VERIFY_ISSUER=shot-crafter-calculator
+# MP_JWT_VERIFY_PUBLICKEY_LOCATION=publicKey.pem
+# SMALLRYE_JWT_SIGN_KEY_LOCATION=privateKey.pem
+# Si queres que el container NO bakee las claves, monta los .pem como volumen:
+#   docker run -v ./keys:/work/keys \
+#     -e MP_JWT_VERIFY_PUBLICKEY_LOCATION=/work/keys/publicKey.pem \
+#     -e SMALLRYE_JWT_SIGN_KEY_LOCATION=/work/keys/privateKey.pem ...
+
+# ===== Cookie =====
+# APP_AUTH_COOKIE_NAME=auth-token
+# APP_AUTH_COOKIE_MAX_AGE_SECONDS=86400
+# APP_AUTH_COOKIE_SECURE=false  # cambiar a true en produccion con HTTPS
+
+# ===== Logging =====
+# QUARKUS_LOG_LEVEL=INFO
+# QUARKUS_LOG_CATEGORY__com_l2_shots=DEBUG
+
+# ===== Ejemplo de uso con persistencia =====
+# docker run -d \
+#   --name shot-crafter \
+#   -p 8080:8080 \
+#   -v /opt/shot-crafter-data:/work/data \
+#   -e QUARKUS_DATASOURCE_JDBC_URL='jdbc:h2:file:/work/data/shots;DB_CLOSE_DELAY=-1' \
+#   -e APP_AUTH_COOKIE_SECURE=true \
+#   gitea.danielarroyo.cl/proyectos/shot-crafter-calculator:latest