fix(studio): retire legacy Style and Grade sections from flat inspector

The flat inspector rendered its new Style/Grade groups AND the legacy
ColorGradingSection/StyleSections components a second time below them,
visibly doubling every control. Remove the now-redundant legacy render
call sites (and their now-unused imports) from PropertyPanelFlat.tsx;
those components stay intact for the legacy (flag-off) PropertyPanel.

packages/studio/src/components/editor/PropertyPanel.test.tsx

@@ -692,6 +692,45 @@ describe("PropertyPanel — Grade group (flag on)", () => {
     },
     RENDER_TIMEOUT_MS,
   );
+
+  it(
+    "does not render the legacy Style/Grade Section duplicates for a style-and-grade-editable element",
+    async () => {
+      // A <video> with no text fields is both style-editable (inherited
+      // capabilities.canEditStyles: true) and grade-editable (tag === "video"),
+      // so both the flat Style and Grade groups render — the exact shape that
+      // used to also mount the legacy ColorGradingSection + StyleSections below
+      // them (the hybrid-duplication bug this task retires).
+      const { host, root } = await renderPanel(true, {
+        ...baseElement(),
+        tagName: "video",
+        textFields: [],
+      });
+      expect(host.textContent).toContain("Style");
+      expect(host.textContent).toContain("Grade");
+      // The legacy `Section` primitive (propertyPanelStyleSections.tsx /
+      // propertyPanelColorGradingSection.tsx) renders a `<section
+      // data-panel-section="<slugified-title>">` for each of its sections. A
+      // bare textContent check can't tell a legacy Section title apart from a
+      // flat row label with the same word — "Fill" is both the legacy Fill
+      // `Section` title AND a row label inside FlatStyleSection, which is
+      // supposed to still be there — so assert on the legacy Section's actual
+      // DOM shape instead of a substring match.
+      for (const slug of [
+        "radius",
+        "stroke",
+        "effects",
+        "clip",
+        "transparency",
+        "fill",
+        "color-grading",
+      ]) {
+        expect(host.querySelector(`[data-panel-section="${slug}"]`)).toBeNull();
+      }
+      act(() => root.unmount());
+    },
+    RENDER_TIMEOUT_MS,
+  );
 });
 
 describe("PropertyPanel — Media group (Plan 4)", () => {

packages/studio/src/components/editor/PropertyPanelFlat.tsx

@@ -14,9 +14,8 @@ import { FlatMotionSection } from "./propertyPanelFlatMotionSection";
 import { FlatMediaSection } from "./propertyPanelFlatMediaSection";
 import { deriveElementTiming } from "./propertyPanelFlatTimingDerivation";
 import { createGsapLivePreview } from "./gsapLivePreview";
-import { formatTextFieldPreview, StyleSections } from "./propertyPanelSections";
+import { formatTextFieldPreview } from "./propertyPanelSections";
 import { STUDIO_GSAP_PANEL_ENABLED } from "./manualEditingAvailability";
-import { ColorGradingSection } from "./propertyPanelColorGradingSection";
 import { useColorGradingController } from "./useColorGradingController";
 import { usePersistedPinnedGroups } from "../../hooks/usePersistedPinnedGroups";
 import {
@@ -55,8 +54,7 @@ const EMPTY_GSAP_EFFECT_HANDLERS = {
  * (same one-directional-import precedent as FlatTextSection). Rendered only
  * when STUDIO_FLAT_INSPECTOR_ENABLED is on; owns the one-open/pin group state.
  *
- * The Text/Style/Layout/Motion/Media groups share the one-open accordion. The
+ * The Text/Style/Layout/Motion/Media/Grade groups share the one-open accordion.
- * legacy Color-Grading section renders unchanged below the flat groups.
  */
 // fallow-ignore-next-line complexity
 export function PropertyPanelFlat({
@@ -502,37 +500,6 @@ export function PropertyPanelFlat({
             {g.content}
           </FlatGroup>
         ))}
-        {sections.colorGrading && (
-          <ColorGradingSection
-            key={[
-              element.id ?? "",
-              element.hfId ?? "",
-              element.selector ?? "",
-              String(element.selectorIndex ?? ""),
-            ].join("|")}
-            projectId={projectId}
-            element={element}
-            assets={assets}
-            previewIframeRef={previewIframeRef}
-            onImportAssets={onImportAssets}
-            onSetAttributeLive={onSetAttributeLive}
-            onApplyScope={onApplyColorGradingScope}
-          />
-        )}
-        {showEditableSections && (
-          <StyleSections
-            projectId={projectId}
-            element={element}
-            styles={styles}
-            assets={assets}
-            onSetStyle={onSetStyle}
-            onImportAssets={onImportAssets}
-            gsapBorderRadius={gsapBorderRadius}
-            // Flex now lives in the flat Layout group (LayoutFlexBlock); suppress
-            // the legacy StyleSections Flex `Section` so it renders exactly once.
-            hideFlex
-          />
-        )}
       </div>
       <PropertyPanelFlatFooter
         onAskAgent={onAskAgent}