feat(view): D4 Design View action family + reapply-on-open wiring

Register toggle/activate/tag/untag/show-both actions driving the D2
shell and D3 model; reapply saved active mode on project load via a
persist load-signal seam. Shared guidString helper; pure nextModeId
unit-tested.

src/view.cpp

@@ -14,13 +14,12 @@
 #include <string>
 #include <vector>
 
+#include "track_guid.h"
 #include "view_tree.h"
 
 #define REAPERAPI_MINIMAL
 #define REAPERAPI_WANT_CountTracks
 #define REAPERAPI_WANT_GetTrack
-#define REAPERAPI_WANT_GetTrackGUID
-#define REAPERAPI_WANT_guidToString
 #define REAPERAPI_WANT_GetMediaTrackInfo_Value
 #define REAPERAPI_WANT_SetMediaTrackInfo_Value
 #define REAPERAPI_WANT_TrackFX_GetCount
@@ -34,17 +33,6 @@ namespace reasampler {
 
 namespace {
 
-// REAPER's GUID -> string form. guidToString needs a 64-byte destination (SDK
-// contract); the canonical "{XXXXXXXX-...}" string is the membership-index key the
-// actions layer tags with, so the tree keys and the model keys align exactly.
-std::string trackGuidString(MediaTrack* tr) {
-    GUID* g = GetTrackGUID(tr);
-    if (!g) return {};
-    char buf[64] = {0};
-    guidToString(g, buf);
-    return std::string(buf);
-}
-
 // The parmname for each planner Flag. All four are documented bool*/int* track
 // info params driven through the double-valued Get/SetMediaTrackInfo_Value API.
 const char* flagParm(Flag f) {
@@ -72,7 +60,7 @@ std::vector<TrackFolderEntry> readFolderEntries(
     for (int i = 0; i < count; ++i) {
         MediaTrack* tr = GetTrack(proj, i);
         if (!tr) continue;
-        std::string guid = trackGuidString(tr);
+        std::string guid = guidString(tr);
         if (guid.empty()) continue;
         int depth = static_cast<int>(GetMediaTrackInfo_Value(tr, "I_FOLDERDEPTH"));
         entries.push_back(TrackFolderEntry{guid, depth});