Setup Maven multi-module project with backend, common, and server modules.

Add `.gitignore` entry for build artifacts.

backend/server/pom.xml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>dev.rheinsw.finlog.backend</groupId>
+        <artifactId>backend</artifactId>
+        <version>${revision}</version>
+    </parent>
+
+    <artifactId>server</artifactId>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <dependencies>
+        <!--    common    -->
+        <dependency>
+            <groupId>dev.rheinsw.finlog.backend</groupId>
+            <artifactId>common</artifactId>
+            <version>${revision}</version>
+            <scope>compile</scope>
+        </dependency>
+    </dependencies>
+
+</project>