Phase 0: test scaffolding + golden fixtures

- ruff config, offscreen smoke tests for all 7 GUI apps/panels
- golden v6 .sras fixtures (complete + 4 truncation variants) generated
  by the pre-refactor writer, with expected header/frontier JSON
- golden geometry fixtures from the pre-refactor _build_scan_params
- consistency tests proving current code reproduces the goldens

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/conftest.py

@@ -0,0 +1,41 @@
+"""Shared test setup: repo-root imports, headless Qt, pyueye stub.
+
+The IDS uEye SDK (pyueye + libueye) only exists on the Linux rig.  On any
+other machine we stub the module before hardware.uc480_camera is imported;
+everything in uc480_camera references `ueye.*` at call time, not import
+time, so an attribute-permissive dummy is sufficient for constructing
+windows and importing modules.
+"""
+import os
+import sys
+import types
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parent.parent
+if str(ROOT) not in sys.path:
+    sys.path.insert(0, str(ROOT))
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+
+try:
+    import pyueye  # noqa: F401
+except ImportError:
+    class _UeyeStub:
+        """Permissive attribute sink standing in for pyueye.ueye."""
+        IS_SUCCESS = 0
+
+        def __getattr__(self, name):
+            return _UeyeStub()
+
+        def __call__(self, *args, **kwargs):
+            return _UeyeStub()
+
+        def __or__(self, other):
+            return 0
+
+        def __ror__(self, other):
+            return 0
+
+    _pyueye = types.ModuleType("pyueye")
+    _pyueye.ueye = _UeyeStub()
+    sys.modules["pyueye"] = _pyueye