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/

src/imports/import_pdb_dialog.h

@@ -0,0 +1,53 @@
+#pragma once
+
+#include <QDialog>
+#include <QVector>
+#include <cstdint>
+
+class QLineEdit;
+class QCheckBox;
+class QListWidget;
+class QLabel;
+class QDialogButtonBox;
+class QPushButton;
+
+namespace rcx {
+
+struct PdbTypeInfo;
+
+class PdbImportDialog : public QDialog {
+    Q_OBJECT
+public:
+    explicit PdbImportDialog(QWidget* parent = nullptr);
+
+    QString pdbPath() const;
+    QVector<uint32_t> selectedTypeIndices() const;
+
+private slots:
+    void browsePdb();
+    void loadPdb();
+    void filterChanged(const QString& text);
+    void selectAllToggled(bool checked);
+    void updateSelectionCount();
+
+private:
+    QLineEdit*        m_pathEdit;
+    QPushButton*      m_browseBtn;
+    QLineEdit*        m_filterEdit;
+    QCheckBox*        m_selectAll;
+    QListWidget*      m_typeList;
+    QLabel*           m_countLabel;
+    QDialogButtonBox* m_buttons;
+
+    struct TypeItem {
+        uint32_t typeIndex;
+        QString  name;
+        int      childCount;
+        bool     isUnion;
+    };
+    QVector<TypeItem> m_allTypes;
+
+    void populateList();
+};
+
+} // namespace rcx