Update build reference to Tycho 5.0.3

Author: carstenartur

.github/copilot-ref-build.md

@@ -10,7 +10,7 @@ export PATH=$JAVA_HOME/bin:$PATH
 java -version  # Must show "21"
 ```
 
-**Why**: Tycho 5.0.1 and Eclipse 2025-12 require Java 21 (class file version 65.0).
+**Why**: Tycho 5.0.3 and Eclipse 2025-12 require Java 21 (class file version 65.0).
 If you see `UnsupportedClassVersionError`, you're using Java 17 instead of 21.
 
 ## Maven Profiles
@@ -67,4 +67,4 @@ Defined in `sandbox_target/eclipse.target`:
 | Tycho resolution errors | Target platform issue | Check `sandbox_target/eclipse.target` |
 | SpotBugs failures | Code quality issue | Check `spotbugs-exclude.xml` |
 | Unused import errors | Tycho treats as errors | Remove all unused imports |
-| Missing NLS comments | Eclipse plugin requirement | Add `//$NON-NLS-1$` to string literals |
+| Missing NLS comments | Eclipse plugin requirement | Add `//$NON-NLS-1$` to string literals |