Retire MPE scaffold; stand up reaper_reasampler pure-core skeleton

Rename CMake project/module to reaper_reasampler, delete mpe_model/mpe_view,
add minimal pure bank_model lib + placeholder CTest. main.cpp loads, logs to
console, keeps the action-registration seam commented with the forever-stable
CEREBELLUM_REASAMPLER_ action-id prefix.

src/main.cpp

@@ -0,0 +1,83 @@
+// main.cpp — the SINGLE translation unit that OWNS the REAPER API pointers.
+//
+// This file is the entire contract between REAPER and the extension:
+//   * At startup REAPER scans UserPlugins/ for reaper_*.dll|dylib|so and
+//     dlopen()s each one, then looks up ONE exported symbol: ReaperPluginEntry
+//     (that name is produced by the REAPER_PLUGIN_ENTRYPOINT macro).
+//   * REAPER calls it, handing over `rec` — a small dispatch struct.
+//       - rec->GetFunc(name)      resolves any REAPER API function to a pointer
+//       - rec->Register(what,ptr) plugs OUR callbacks into REAPER
+//   * REAPERAPI_LoadAPI(rec->GetFunc) walks reaper_plugin_functions.h and
+//     fills in every global function pointer (ShowConsoleMsg, InsertMedia...).
+//
+// Exactly ONE .cpp defines REAPERAPI_IMPLEMENT (this one) — that allocates
+// storage for those global pointers. Every other .cpp includes
+// reaper_plugin_functions.h WITHOUT the define and gets `extern` declarations.
+
+#define REAPERAPI_IMPLEMENT
+#include "reaper_plugin.h"
+#include "reaper_plugin_functions.h"
+
+// Persistent action-id prefix for the ReaSampler action family.
+// Every bindable action (capture / insert / slot / verify) mints its command id
+// from a string beginning with this prefix, e.g. "CEREBELLUM_REASAMPLER_CAPTURE_MASTER".
+// FOREVER-STABLE once shipped: user keybindings key off these strings, so the
+// prefix and any minted id must never change after release.
+#define REASAMPLER_ACTION_PREFIX "CEREBELLUM_REASAMPLER_"
+
+// Globals other files reference via `extern`.
+REAPER_PLUGIN_HINSTANCE g_hInst = nullptr;  // this module's instance handle
+reaper_plugin_info_t*   g_rec   = nullptr;  // REAPER's dispatch struct
+
+// ---- Action registration seam (reusable pattern, no action wired yet) ------
+// The capture/insert/slot action family (PLAN.md M3+) reinstates the pattern
+// below. Kept as a commented template so the shape is not re-derived each time.
+//
+// static int g_cmdCaptureMaster = 0;
+//
+// // REAPER calls this for EVERY action fired anywhere; claim only your own id,
+// // return false otherwise so REAPER keeps looking.
+// static bool OnHookCommand(int command, int /*flag*/)
+// {
+//     if (command == 0) return false;
+//     if (command == g_cmdCaptureMaster) { /* route to capture module */ return true; }
+//     return false;
+// }
+//
+// Registration, inside the load branch below:
+//   1) g_cmdCaptureMaster =
+//          rec->Register("command_id", (void*)(REASAMPLER_ACTION_PREFIX "CAPTURE_MASTER"));
+//   2) static gaccel_register_t sAccel{};
+//      sAccel.accel.cmd = g_cmdCaptureMaster;
+//      sAccel.desc      = "ReaSampler: capture master mix";
+//      rec->Register("gaccel", (void*)&sAccel);
+//   3) rec->Register("hookcommand", (void*)&OnHookCommand);
+// On unload (rec == nullptr), mirror-unregister with the same strings prefixed '-'.
+
+extern "C" REAPER_PLUGIN_DLL_EXPORT int REAPER_PLUGIN_ENTRYPOINT(
+    REAPER_PLUGIN_HINSTANCE hInstance, reaper_plugin_info_t* rec)
+{
+    if (!rec)
+    {
+        // rec == nullptr  =>  REAPER is UNLOADING us. Mirror-unregister every
+        // callback here (same strings prefixed with '-') once actions are wired.
+        g_rec = nullptr;
+        return 0;
+    }
+
+    // ABI guard: the struct layout we compiled against must match this REAPER.
+    if (rec->caller_version != REAPER_PLUGIN_VERSION)
+        return 0;
+
+    // Resolve every REAPER API function pointer. Returns the number that FAILED
+    // to load; 0 == success. Non-zero usually means REAPER is older than our SDK.
+    if (REAPERAPI_LoadAPI(rec->GetFunc) != 0)
+        return 0;
+
+    g_hInst = hInstance;
+    g_rec   = rec;
+
+    ShowConsoleMsg("ReaSampler loaded.\n");
+
+    return 1;  // success — REAPER keeps us loaded
+}