Restructure into src/ layout under pygui package

Move all application source under src/pygui/ and rewire imports,
build config, and QML module path to match.
- Relocate backend/, serialcomm/, and the ISC QML module into
  src/pygui/; convert main.py into pygui/__main__.py with a main()
  entry point (run via `python -m pygui` or the new `isc` script)
- Rewrite absolute imports: backend.* -> pygui.backend.*,
  serialcomm.* -> pygui.serialcomm.* (source + tests)
- Move app icons (isc.ico/icns) into packaging/
- Update README and ISC.qmlproject to the new paths

pyproject.toml

@@ -1,3 +1,8 @@
+# ===== Build System =====
+[build-system]
+requires = ["setuptools>=61"]
+build-backend = "setuptools.build_meta"
+
 # ===== Project Metadata =====
 [project]
 name = "pygui"
@@ -6,9 +11,50 @@ version = "0.1.0"
 [project.optional-dependencies]
 dev = ["pytest"]
 
+# ===== Console Entry Point =====
+[project.scripts]
+isc = "pygui.__main__:main"
+
+# ===== Package Discovery (src layout) =====
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.setuptools.package-data]
+# Ship the QML module alongside the Python package.
+pygui = ["ISC/**/*.qml", "ISC/**/qmldir"]
+
 # ===== PySide Build Inputs =====
 [tool.pyside6-project]
-files = ["ISC/HomePage.qml", "ISC/Main.qml", "ISC/Tabs/DataTab.qml", "ISC/Tabs/GraphTab.qml", "ISC/Tabs/SelectFileDialog.qml", "ISC/Tabs/SettingsTab.qml", "ISC/Tabs/StatusTab.qml", "ISC/Tabs/qmldir", "ISC/Theme.qml", "ISC/qmldir", "backend/data_model.py", "backend/device_controller.py", "backend/graph_view.py", "backend/file_browser.py", "backend/local_settings.py", "backend/local_settings_model.py", "main.py", "serialcomm/__init__.py", "serialcomm/data_parser.py", "serialcomm/serial_port.py", "serialcomm/device_service.py"]
+files = [
+    "src/pygui/ISC/HomePage.qml",
+    "src/pygui/ISC/Main.qml",
+    "src/pygui/ISC/Theme.qml",
+    "src/pygui/ISC/qmldir",
+    "src/pygui/ISC/Tabs/DataTab.qml",
+    "src/pygui/ISC/Tabs/SelectFileDialog.qml",
+    "src/pygui/ISC/Tabs/SettingsTab.qml",
+    "src/pygui/ISC/Tabs/StatusTab.qml",
+    "src/pygui/ISC/Tabs/qmldir",
+    "src/pygui/__main__.py",
+    "src/pygui/backend/contour_models.py",
+    "src/pygui/backend/crypto_helper.py",
+    "src/pygui/backend/csv_file_metadata.py",
+    "src/pygui/backend/data_model.py",
+    "src/pygui/backend/data_segment.py",
+    "src/pygui/backend/device_controller.py",
+    "src/pygui/backend/file_browser.py",
+    "src/pygui/backend/frame.py",
+    "src/pygui/backend/graph_view.py",
+    "src/pygui/backend/local_settings.py",
+    "src/pygui/backend/local_settings_model.py",
+    "src/pygui/backend/marching_squares.py",
+    "src/pygui/backend/zwafer_models.py",
+    "src/pygui/backend/zwafer_parser.py",
+    "src/pygui/serialcomm/__init__.py",
+    "src/pygui/serialcomm/data_parser.py",
+    "src/pygui/serialcomm/device_service.py",
+    "src/pygui/serialcomm/serial_port.py",
+]
 
 [dependency-groups]
 dev = [