build: split core/ from frontends/; prepare for multiple GUI/TUI targets

Reorganise the tree into business vs frontend as separate directories:
  src/core/{domain,imports,app}   (was system/, imports/, app/)
  src/frontends/tui/              (was tui/ + main.cpp)
  tests/tui/                      (the FTXUI-coupled helper test)
All cross-dir #include paths rewritten; same-dir includes untouched.

CMake: essim_core is the frontend-agnostic business library — links libzip,
pugixml and bsdl, NO GUI toolkit. Each frontend is a self-contained
src/frontends/<name>/ (own CMakeLists, toolkit, main.cpp) that links
essim_core, selected with -DESSIM_FRONTEND=<name> (default tui; 'none' = core +
tests only, no toolkit fetched). FTXUI moved into the tui frontend. Tests are
split: essim_tests links essim_core (no FTXUI), essim_tui_tests links essim_tui.

Verified: default tui build green (ctest 2/2); ESSIM_FRONTEND=none builds the
core + tests with FTXUI never fetched and no `essim` binary.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_analysis.cpp

@@ -1,11 +1,11 @@
 #include <doctest/doctest.h>
 
-#include "system/analysis.hpp"
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/analysis.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
 
 #include <memory>
 #include <string>

tests/test_bsdl_apply.cpp

@@ -1,14 +1,14 @@
 #include <doctest/doctest.h>
 
-#include "system/analysis.hpp"
-#include "system/bsdl_check.hpp"
-#include "system/bsdl_model.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/pin_spec.hpp"
-#include "system/system.hpp"
-#include "system/modules.hpp"
-#include "system/persist.hpp"
+#include "core/domain/analysis.hpp"
+#include "core/domain/bsdl_check.hpp"
+#include "core/domain/bsdl_model.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/pin_spec.hpp"
+#include "core/domain/system.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/persist.hpp"
 
 #include <cstdio>
 #include <fstream>

tests/test_bsdl_check.cpp

@@ -1,13 +1,13 @@
 #include <doctest/doctest.h>
 
-#include "system/analysis.hpp"
-#include "system/bsdl_check.hpp"
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/pin_spec.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/analysis.hpp"
+#include "core/domain/bsdl_check.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pin_spec.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
 
 #include <algorithm>
 #include <vector>

tests/test_component_kind.cpp

@@ -1,7 +1,7 @@
 #include <doctest/doctest.h>
 
-#include "system/component_kind.hpp"
-#include "system/parts.hpp"
+#include "core/domain/component_kind.hpp"
+#include "core/domain/parts.hpp"
 
 #include <memory>
 

tests/test_export.cpp

@@ -1,12 +1,12 @@
 #include <doctest/doctest.h>
 
-#include "app/export.hpp"
-#include "system/connect.hpp"
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/app/export.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
 
 #include <cstdio>
 #include <fstream>

tests/test_nc_origin.cpp

@@ -1,11 +1,11 @@
 #include <doctest/doctest.h>
 
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/persist.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/persist.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
 
 #include <filesystem>
 #include <memory>

tests/test_persist.cpp

@@ -1,12 +1,12 @@
 #include <doctest/doctest.h>
 
-#include "system/connect.hpp"
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/persist.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/persist.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
 
 #include <filesystem>
 #include <memory>

tests/test_pin_model.cpp

@@ -1,9 +1,9 @@
 #include <doctest/doctest.h>
 
-#include "system/parts.hpp"
-#include "system/pin_model.hpp"
-#include "system/pin_spec.hpp"
-#include "system/pins.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pin_model.hpp"
+#include "core/domain/pin_spec.hpp"
+#include "core/domain/pins.hpp"
 
 #include <string>
 #include <vector>

tests/test_pin_name.cpp

@@ -1,9 +1,9 @@
 #include <doctest/doctest.h>
 
-#include "system/parts.hpp"
-#include "system/pin_name.hpp"
-#include "system/pins.hpp"
-#include "system/transform.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pin_name.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/transform.hpp"
 
 #include <memory>
 

tests/test_signal_type.cpp

@@ -1,6 +1,6 @@
 #include <doctest/doctest.h>
 
-#include "system/signal_type.hpp"
+#include "core/domain/signal_type.hpp"
 
 TEST_CASE("signal_type_name round-trips with from_name") {
     SignalType t;

tests/test_vpx_transform.cpp

@@ -1,12 +1,12 @@
 #include <doctest/doctest.h>
 
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
-#include "system/transform.hpp"
-#include "system/transform_vpx.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
+#include "core/domain/transform.hpp"
+#include "core/domain/transform_vpx.hpp"
 
 #include <map>
 #include <memory>

tests/tui/test_helpers.cpp

@@ -1,6 +1,6 @@
 #include <doctest/doctest.h>
 
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui_helpers.hpp"
 
 #include <algorithm>
 #include <vector>