Add organising module: DisplayNameGenerator/@Nested/@Tag demos on JUnit 6.1.3

Companion code for the rewritten post "Organising and Displaying JUnit Tests:
@DisplayName, @Nested, @Tag (JUnit 5 -> JUnit 6)". Same suite also runs green
on JUnit 5.14.4 via -Djunit.version. Verified, not assumed: GA dates and
versions cross-checked against Maven Central metadata and docs.junit.org
release notes; the @TestMethodOrder-inheritance-into-@Nested-classes and
MethodOrderer.Default/ClassOrderer.Default behaviour differences between
5.14.4 and 6.1.3 are demonstrated by actually running the same source under
both engines (see organising/output/12-* and 14-*), not by reading about them.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01YXCrLgRKFgCh9RHKW8xaqJ

organising/output/16-broken-compile-junit5.14.4.txt

@@ -0,0 +1,8 @@
+$ javac -cp <junit-jupiter-5.14.4 and its dependencies> src/broken/MethodOrdererDefaultDemo.java
+Picked up JAVA_TOOL_OPTIONS: -Djavax.net.ssl.trustStore=/etc/ssl/certs/java/cacerts -Djavax.net.ssl.trustStoreType=JKS -Dhttps.proxyHost=127.0.0.1 -Dhttps.proxyPort=36237 -Dhttp.nonProxyHosts=localhost|127.0.0.1|::1|127.*|0.*|::|169.254.*|api.anthropic.com|api-staging.anthropic.com|api-pr-preview.anthropic.com|mcp-proxy.anthropic.com|mcp-proxy-staging.anthropic.com|registry.npmjs.org|jsr.io|npm.jsr.io|pypi.org|files.pythonhosted.org|index.crates.io|proxy.golang.org|host.docker.internal|10.*|172.16.*|172.17.*|172.18.*|172.19.*|172.20.*|172.21.*|172.22.*|172.23.*|172.24.*|172.25.*|172.26.*|172.27.*|172.28.*|172.29.*|172.30.*|172.31.*|192.168.*|100.64.0.0/10|*.svc.cluster.local|*.svc.cluster.local -Djdk.http.auth.tunneling.disabledSchemes= -Djdk.http.auth.proxying.disabledSchemes=
+src/broken/MethodOrdererDefaultDemo.java:22: error: cannot find symbol
+    @TestMethodOrder(MethodOrderer.Default.class) // <-- does not exist before JUnit 6.0
+                                  ^
+  symbol:   class Default
+  location: interface MethodOrderer
+1 error