build: prepare DDK release 19.3.0

[joaodinissf]

Why the change

The release workflow only releases when every feature declares the release version, so both features move to 19.3.0 for the next DDK release.

Special things to note

• 19.3.0 rather than 19.2.1: the release moves the target platform to Eclipse 2026-09 (build: target update to Eclipse 2026-09 #1558) and completes the Xtend to Java migration, which is more than a fixes-only patch.
• Same five files and same shape as bd137db, the preparation of 19.2.0. The release is then release.yml with branch=master, version_bump=minor: v19.2.0 → v19.3.0.
• Merge last, after build: target update to Eclipse 2026-09 #1558, fix(export,scope): record the Java types a model names as dependencies #1556 and (if approved) perf(scope,export): reuse the model type resolver, class loader and genmodel lookups within a generation pass #1547, each at least a minute apart: they all change the runtime feature's version.

Change outline

 com.avaloq.tools.ddk.feature/feature.xml          19.2.1.qualifier → 19.3.0.qualifier
 com.avaloq.tools.ddk.feature/pom.xml              19.2.1-SNAPSHOT  → 19.3.0-SNAPSHOT
 com.avaloq.tools.ddk.runtime.feature/feature.xml  19.2.1.qualifier → 19.3.0.qualifier
 com.avaloq.tools.ddk.runtime.feature/pom.xml      19.2.1-SNAPSHOT  → 19.3.0-SNAPSHOT
 ddk-repository/category.xml                       both feature pins (url and version) → 19.3.0

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