feat(vst): stand up VST3 instrument spike (S1) — skeleton, IPlugView↔LICE editor, REAPER bridge read

Vendor Steinberg VST3 SDK (v3.7.9_build_61); add reasampler_vst.vst3 as a second, additive build artifact with pure editor-geometry + bridge-marshal helpers under CTest.

src/vst/reasampler_editor.h

@@ -0,0 +1,65 @@
+// reasampler_editor.h — the VST3 IPlugView LICE editor (Phase S1 bridge spike). THIN
+// shell: hosts a LICE-drawn child window inside the host's IPlugView seat and routes
+// host paint/click into the pure editor_geometry hit-test. Windows-only (D5).
+//
+// This is the phase's ONE genuine unknown (per CONTEXT.md §Phase S / S1): wiring LICE
+// into an IPlugView. It reuses the bank_panel LICE/SWELL competence — a LICE_SysBitmap
+// blitted in WM_PAINT, GET_X/Y_LPARAM hit-testing in WM_LBUTTONDOWN — but hangs it off a
+// child HWND created in IPlugView::attached() rather than a docked SWELL dialog.
+//
+// Subclasses CPluginView (public.sdk/source/common/pluginview.h) for the IPlugView
+// refcount + attached/removed/getSize/onSize boilerplate; we override the attach/remove
+// hooks to create/destroy the child window and onSize to resize it.
+
+#pragma once
+
+#include "public.sdk/source/common/pluginview.h"
+
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
+namespace reasampler::vst {
+
+class ReaperBridge;
+
+class ReaSamplerEditor : public Steinberg::CPluginView {
+public:
+    // `bridge` is owned by the processor and outlives the editor; the editor reads
+    // (never mutates) it to show a live-state readout. May be null (non-REAPER host).
+    explicit ReaSamplerEditor(ReaperBridge* bridge);
+    ~ReaSamplerEditor() override;
+
+    // Accept only the Windows HWND platform type (D5: Windows-only).
+    Steinberg::tresult PLUGIN_API isPlatformTypeSupported(
+        Steinberg::FIDString type) override;
+
+    // The view is user-resizable in the spike so we exercise the onSize path.
+    Steinberg::tresult PLUGIN_API canResize() override;
+
+protected:
+    // CPluginView hooks: systemWindow is set by the time attachedToParent() fires.
+    void attachedToParent() override;
+    void removedFromParent() override;
+
+    Steinberg::tresult PLUGIN_API onSize(Steinberg::ViewRect* newSize) override;
+
+private:
+#ifdef _WIN32
+    // Draw the current surface into the child window's DC via a LICE bitmap.
+    void paint(HDC hdc);
+    // Route a client-space click through editor_geometry::hitTest.
+    void onClick(int x, int y);
+
+    static LRESULT CALLBACK wndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam);
+
+    HWND childHwnd_ = nullptr;
+#endif
+
+    ReaperBridge* bridge_ = nullptr;
+    // Latched on click so the paint reflects the last hit-test result — the spike's
+    // proof that host->click->draw routing round-trips.
+    bool buttonHit_ = false;
+};
+
+}  // namespace reasampler::vst