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/

third_party/raw_pdb/CMakeLists.txt

@@ -0,0 +1,9 @@
+cmake_minimum_required(VERSION 3.16)
+
+project(raw_pdb)
+
+set(CMAKE_CXX_STANDARD 11)
+
+set_property(GLOBAL PROPERTY USE_FOLDERS ON)
+
+add_subdirectory(src)