feat: PDB import via RawPDB, no msdia140.dll dependency

Replace DIA SDK COM-based PDB importer with RawPDB (MolecularMatters)
which reads PDB files directly via memory-mapped I/O. Adds File menu
"Import PDB..." dialog with type filtering, selection, and progress.

- Vendor raw_pdb into third_party/
- Two-phase API: enumeratePdbTypes() + importPdbSelected()
- Full recursive import of structs/unions/arrays/pointers/bitfields
- PDB import dialog with name filter, select-all, type count
- Benchmark: 1654 types from ntkrnlmp.pdb in 16ms
- Reorganize import/export files into src/imports/

tests/test_export_xml.cpp

@@ -1,8 +1,8 @@
 #include <QtTest/QtTest>
 #include <QTemporaryFile>
 #include "core.h"
-#include "export_reclass_xml.h"
-#include "import_reclass_xml.h"
+#include "imports/export_reclass_xml.h"
+#include "imports/import_reclass_xml.h"
 
 using namespace rcx;