Remove forward-declaration stub-header directories (.forward-declarations/, forward-declarations/)

Deletes the two stub-header trees (249 files) that shadowed the real
rtiddsgen-generated DDS headers, and removes every reference to them.

CMake (15 include-path entries):
  root CMakeLists.txt include_directories(.../forward-declarations);
  NGL_TARGET_INCLUDE_DIRECTORIES entries in 7 service CMakeLists
  (ServiceManagement, SoundManagement, SituationMap, ScreenRecording,
   SituationReplayManagement, SituationReplay, ServiceMonitor)

Source includes that resolved to the root-level stubs (only 2, repointed to the
module-prefixed generated headers the rest of the tree already uses):
  Lts/Services/AreaEffectSimulation/object_charge_effect.h
    <aes_dtc.h> -> <AreaEffectSimulation/aes_dtc.h>
  Lts/Proxies/TrainingAreaBaseOC/websocket_handler.h
    <taboc_dtc.h> -> <TrainingAreaBaseOC/taboc_dtc.h>
  (generic_dtc_impl.h needs no change: its quote-include "generic_dtc.h"
   resolves to the real Lts/DDS/DTC/generic_dtc.h in the same directory)

Tests:
  tests/test_migration_stubs.cpp: remove the redundant root-level stub test
    (AesDtcCompiles) - the module-prefixed AreaEffectSimulationDtcCompiles test
    already exercises the same AreaEffectSimulation::Interface header.
  tests/test_skl_dtc.cpp: delete (removed-module compile test, already filtered
    out of the build) and remove its now-obsolete CMake list(FILTER) exclusion.

Validation: full rebuild (build4, make -j4 -k) with the removal - 0 new compile
errors vs the pre-existing base-state baseline (77 unique real-error signatures
identical to baseline; all 15 'No such file' headers pre-existing).

qt6-after/qt6-migrated-legatus/tests/test_migration_stubs.cpp

@@ -216,12 +216,3 @@ TEST(MigrationStubs, GenericDtcCompiles)
     // Verify GenericDtc template is accessible
     EXPECT_TRUE(true);
 }
-
-// AES DTC (root level) - uses AreaEffectSimulation::Interface namespace
-#include "aes_dtc.h"
-
-TEST(MigrationStubs, AesDtcCompiles)
-{
-    using namespace AreaEffectSimulation::Interface;
-    EXPECT_TRUE(true);
-}