Ψ-W1-T2 review remediation: solo restore drops on visible-in-target, not parked; N-mode segments read dead when unroutable

Fixes a hidden-parent solo replay that could silence the mix. Also closes the N-mode segment silent no-op, amends the invariant comment, trims view.cpp under 600 lines, hedges two SDK inferences, drops a dead null-check.

src/core/ui/footer_bar.cpp

@@ -64,8 +64,8 @@ FooterHit hitTestFooterBar(int px, int py, const FooterBarLayout& layout) {
     return FooterHit::None;
 }
 
-bool modeSegmentEnabled(bool isActiveSegment, bool transportRunning) {
-    return isActiveSegment || !transportRunning;
+bool modeSegmentEnabled(bool isActiveSegment, bool transportRunning, bool routable) {
+    return isActiveSegment || (!transportRunning && routable);
 }
 
 } // namespace reasampler::ui