feat: add waveform scope view with resizable divider

- Create primitives.h/c for waveform visualization (time/amplitude display)
- Scope view draws signal as per-pixel min/max envelope (Audacity-style)
- Add draggable divider between spectrogram and scope (30%-80% range)
- Fix selection bounds to use correct spectrogram area (not full viewport)
- Scope syncs with spectrogram zoom/pan for aligned time axis

rspektrum.make

@@ -121,9 +121,11 @@ OBJECTS :=
 GENERATED += $(OBJDIR)/spectrogram.o
 GENERATED += $(OBJDIR)/platform_linux.o
 GENERATED += $(OBJDIR)/utils.o
+GENERATED += $(OBJDIR)/primitives.o
 OBJECTS += $(OBJDIR)/spectrogram.o
 OBJECTS += $(OBJDIR)/platform_linux.o
 OBJECTS += $(OBJDIR)/utils.o
+OBJECTS += $(OBJDIR)/primitives.o
 
 # Rules
 # #############################################
@@ -199,6 +201,10 @@ $(OBJDIR)/utils.o: src/utils.c
 	@echo "$(notdir $<)"
 	$(SILENT) $(CC) $(ALL_CFLAGS) $(FORCE_INCLUDE) -o "$@" -MF "$(@:%.o=%.d)" -c "$<"
 
+$(OBJDIR)/primitives.o: src/primitives.c
+	@echo "$(notdir $<)"
+	$(SILENT) $(CC) $(ALL_CFLAGS) $(FORCE_INCLUDE) -o "$@" -MF "$(@:%.o=%.d)" -c "$<"
+
 -include $(OBJECTS:%.o=%.d)
 ifneq (,$(PCH))
   -include $(PCH_PLACEHOLDER).d