fix(analytics): upgrade Spark to 4.0.3 — 3.5.x has no official Docker image

apache/spark:3.5.4-scala2.13-java17-ubuntu does not exist on Docker Hub.
Oldest available scala2.13 image is 4.0.3. Bump compileOnly deps and
Dockerfile base image to match.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/analytics/build.gradle.kts

@@ -42,7 +42,7 @@ scala {
     scalaVersion = versions["SCALA3"]!!
 }
 
-val sparkVersion = "3.5.4"
+val sparkVersion = "4.0.3"
 
 dependencies {
     compileOnly("org.scala-lang:scala3-compiler_3") {

modules/analytics/src/main/docker/Dockerfile

@@ -1,4 +1,4 @@
-FROM apache/spark:3.5.4-scala2.13-java17-ubuntu
+FROM apache/spark:4.0.3-scala2.13-java17-ubuntu
 
 USER root