Ψ-W1-T2: disjoint per-mode solo surfaces and a playback-gated mode switch

Solo is cached, cleared and replayed per mode on a real switch only; the switch is refused visibly while the transport runs. The footer segment now routes through the activate actions, so a panel switch finally persists.

src/shell/view/view.h

@@ -14,10 +14,19 @@ class ReaProject;
 
 namespace reasampler {
 
-// Snapshots each about-to-park track's flags into `model`, runs planToggle,
-// applies park/restore writes plus parent visibility flags, then sets the
-// active mode. Wrapped in one Undo block. Returns false (no mutation) if
-// `targetModeId` isn't registered. `proj` == nullptr means the current project.
+// True while `proj`'s transport is playing or recording — the condition under which
+// applyMode refuses a real mode switch. Exposed so the panel can paint the footer's
+// [Arrange|Design] segments disabled BEFORE the click rather than only refusing on
+// it. `proj` == nullptr means the current project.
+bool transportBlocksModeSwitch(ReaProject* proj);
+
+// Snapshots each about-to-park track's flags into `model`, caches/clears the
+// outgoing mode's solo state and replays the incoming mode's, runs planToggle,
+// applies park/restore writes plus parent visibility flags, then sets the active
+// mode. Wrapped in one Undo block. Returns false (no mutation) if `targetModeId`
+// isn't registered, or if this is a real switch (target != active) while the
+// transport is running. A reapply (target == active) is never gated and never
+// touches solo. `proj` == nullptr means the current project.
 bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject* proj);
 
 // Splits any track visible in more than one mode while carrying its own media