filter: sweep the corner continuously; raise the editor floor to 840x620

Cutoff-only re-solve (15.5 vs 56.9 ns/frame) makes the unquantized sweep
affordable, replacing the 2048-step mod quantizer. Live-compute parameters
remain blocked on a shell-architecture ruling.

src/shell/instrument/editor_session.cpp

@@ -38,10 +38,9 @@ using util::readFileBytes;
 
 ReaSamplerEditor::ReaSamplerEditor(ReaSamplerProcessor* processor)
     : CPluginView(nullptr), processor_(processor) {
-    // Default view size, tuned to the band heights: chrome + two-lane waveform + the deck
-    // (now two rows since the filter group). 840x620 clears the full face without scroll on
-    // 1080p.
-    ViewRect r(0, 0, 840, 620);
+    // The default IS the enforced floor (checkSizeConstraint) — the face opens at the size its
+    // band stack is laid out for and can only be grown from there.
+    ViewRect r(0, 0, instrument::ui::kEditorMinWidth, instrument::ui::kEditorMinHeight);
     setRect(r);
 }