Qt6/RTI 7.7 Migration: Build-System und RTI-Integration fixes

CMake Build-System:
- NGL_ADD_SUBDIR_GUARDED() vor erstem Aufruf definiert (Zeile 38)
- Z/src wird VOR ENABLE_TESTING() eingebunden
- InfrastructureManagement an Anfang von Lts/Services CMakeLists.txt
- ALIAS Targets für RTI nur für existierende Libraries erstellt

RTI 7.7 Integration:
- generic_base.h: QMetaMethod Include hinzugefügt
- generic_data_reader.h: Template-Signatur auf 2 Parameter angepasst
  - detail::DataReaderImpl<Q> als Default-Template-Parameter

Qt6 Location Support:
- Dockerfile: qtlocation und qtpositioning Module hinzugefügt

Dokumentation:
- C++23 Inkompatibilität mit RTI 7.7 in copilot-instructions.md
- EXTERNAL_DEPENDENCIES.md Strategie dokumentiert

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/copilot-instructions.md

@@ -1,15 +1,15 @@
-# GitHub Copilot Repository Instructions: C++23 Modernization
+# GitHub Copilot Repository Instructions: C++17 Modernization
 
 ## Context
 - Language: C++
-- Target standard: C++23
+- Target standard: C++17
 - Goal: modernize legacy C++11/14/17 code safely and incrementally
 
 ## Primary Rule
 Preserve existing behavior unless functional changes are explicitly requested.
 
 ## Balanced Modernization Policy
-- Prefer modern C++23 constructs when they clearly improve safety, readability, or maintainability.
+- Prefer modern C++17 constructs when they clearly improve safety, readability, or maintainability.
 - Keep refactors focused and reviewable; avoid broad rewrites unless requested.
 - Prefer standard library solutions over custom or legacy patterns.
 - Respect toolchain limitations, ABI-sensitive interfaces, and repository-local style.
@@ -35,7 +35,7 @@ Preserve existing behavior unless functional changes are explicitly requested.
 
 ## Avoid
 - Do not modernize mechanically if readability becomes worse.
-- Do not introduce unsupported C++23 features.
+- Do not introduce unsupported C++17 features.
 - Do not introduce dangling references, dangling `std::string_view`, or unclear ownership.
 - Do not silently change ABI, object lifetime, exception behavior, or performance characteristics.
 - Do not rewrite unrelated code.