refactor(game): extract EntityController from GameHandler (step 1.3)

Moves entity lifecycle, name/creature/game-object caches, transport GUID
tracking, and the entire update-object pipeline out of GameHandler into a
new EntityController class (friend-class pattern, same as CombatHandler
et al.).

What moved:
- applyUpdateObjectBlock() — 1,520-line core of all entity creation,
  field updates, and movement application
- processOutOfRangeObjects() / finalizeUpdateObjectBatch()
- handleUpdateObject() / handleCompressedUpdateObject() / handleDestroyObject()
- handleNameQueryResponse() / handleCreatureQueryResponse()
- handleGameObjectQueryResponse() / handleGameObjectPageText()
- handlePageTextQueryResponse()
- enqueueUpdateObjectWork() / processPendingUpdateObjectWork()
- playerNameCache, playerClassRaceCache_, pendingNameQueries
- creatureInfoCache, pendingCreatureQueries
- gameObjectInfoCache_, pendingGameObjectQueries_
- transportGuids_, serverUpdatedTransportGuids_
- EntityManager (accessed by other handlers via getEntityManager())

8 opcodes re-registered by EntityController::registerOpcodes():
  SMSG_UPDATE_OBJECT, SMSG_COMPRESSED_UPDATE_OBJECT, SMSG_DESTROY_OBJECT,
  SMSG_NAME_QUERY_RESPONSE, SMSG_CREATURE_QUERY_RESPONSE,
  SMSG_GAMEOBJECT_QUERY_RESPONSE, SMSG_GAMEOBJECT_PAGETEXT,
  SMSG_PAGE_TEXT_QUERY_RESPONSE

Other handler files (combat, movement, social, spell, inventory, quest,
chat) updated to access EntityManager via getEntityManager() and the
name cache via getPlayerNameCache() — no logic changes.

Also included:
- .clang-tidy: add modernize-use-nodiscard,
  modernize-use-designated-initializers; set -std=c++20 in ExtraArgs
- test.sh: prepend clang's own resource include dir before GCC's to
  silence xmmintrin.h / ia32intrin.h conflicts during clang-tidy runs

Line counts:
  entity_controller.hpp  147 lines  (new)
  entity_controller.cpp  2172 lines (new)
  game_handler.cpp       8095 lines (was 10143, −2048)

Build: 0 errors, 0 warnings.

test.sh

@@ -75,8 +75,19 @@ echo "Linting ${#SOURCE_FILES[@]} source files..."
 EXTRA_TIDY_ARGS=()   # for direct clang-tidy:  --extra-arg=...
 EXTRA_RUN_ARGS=()    # for run-clang-tidy:     -extra-arg=...
 if command -v gcc >/dev/null 2>&1; then
+    # Prepend clang's own resource include dir first so clang uses its own
+    # versions of xmmintrin.h, ia32intrin.h, etc. rather than GCC's.
+    clang_resource_inc="$($CLANG_TIDY -print-resource-dir 2>/dev/null || true)/include"
+    if [[ -d "$clang_resource_inc" ]]; then
+        EXTRA_TIDY_ARGS+=("--extra-arg=-isystem${clang_resource_inc}")
+        EXTRA_RUN_ARGS+=("-extra-arg=-isystem${clang_resource_inc}")
+    fi
+
     while IFS= read -r inc_path; do
         [[ -d "$inc_path" ]] || continue
+        # Skip the GCC compiler built-in include dir — clang's resource dir above
+        # provides compatible replacements for xmmintrin.h, ia32intrin.h, etc.
+        [[ "$inc_path" == */gcc/* ]] && continue
         EXTRA_TIDY_ARGS+=("--extra-arg=-isystem${inc_path}")
         EXTRA_RUN_ARGS+=("-extra-arg=-isystem${inc_path}")
     done < <(