fix(tradein/v2): keep top nav active over overlays, stronger «К оценке», backdrop-close

Three UX fixes on the /trade-in/v2 overlays (feedback):

1. TopNav stays interactive while a section overlay is open. The a11y
   audit #2081 put inert on the whole content wrap (which contains
   TopNav), so opening an overlay disabled the top tabs. Move inert off
   the wrap onto <main>/<footer> only; the nav is inert just for the
   full-screen LocationDrawer. Users can now switch sections directly
   from an open overlay. role=dialog/aria-modal/Esc/focus-trap kept.

2. «← К ОЦЕНКЕ» made a clear filled primary button (solid accentDeep bg,
   white text ≥4.9:1 AA, shadow, hover lift) instead of the weak ghost
   pill. Uses existing accent tokens only.

3. Backdrop click closes the overlay. Add a transparent sibling layer
   below the panel (z below it, starting under the nav so tabs stay
   clickable); clicks in the margin close it. Clicks inside the panel /
   on its buttons never reach it (sibling, not ancestor) so they don't
   close. Esc + focus restore preserved.

tradein-mvp/frontend/src/app/v2/page.tsx

@@ -701,7 +701,6 @@ export default function TradeInV2Page() {
 
         {/* CONTENT WRAP */}
         <div
-          inert={nav !== 0 || drawerOpen ? true : undefined}
           style={{
             position: "absolute",
             inset: 14,
@@ -710,7 +709,17 @@ export default function TradeInV2Page() {
             flexDirection: "column",
           }}
         >
-          <nav aria-label="Разделы" style={{ display: "contents" }}>
+          {/* TopNav stays interactive while a section overlay is open so the
+              user can switch sections directly from the overlay. Only the
+              LocationDrawer (a full modal over the whole HUD) inerts it. The
+              dashboard body (<main>/<footer>) is still inerted behind ANY
+              overlay/drawer — preserving the focus + click guard from a11y
+              audit #2081 for everything except the top tabs. */}
+          <nav
+            aria-label="Разделы"
+            inert={drawerOpen ? true : undefined}
+            style={{ display: "contents" }}
+          >
             <TopNav
               active={nav}
               onNavigate={setNav}
@@ -719,7 +728,10 @@ export default function TradeInV2Page() {
               onLogout={logout}
             />
           </nav>
-          <main style={{ display: "contents" }}>
+          <main
+            inert={nav !== 0 || drawerOpen ? true : undefined}
+            style={{ display: "contents" }}
+          >
             <HeroBar
               data={{ report, object: objectInfo }}
               estimateId={mounted ? currentEstimateId : null}
@@ -749,7 +761,10 @@ export default function TradeInV2Page() {
             </div>
           </main>
 
-          <footer style={{ display: "contents" }}>
+          <footer
+            inert={nav !== 0 || drawerOpen ? true : undefined}
+            style={{ display: "contents" }}
+          >
             <Footer data={report} hasEstimate={hasEstimate} />
           </footer>
         </div>

tradein-mvp/frontend/src/components/trade-in/v2/SectionOverlay.tsx

@@ -30,6 +30,11 @@ interface SectionOverlayProps {
   cache?: CacheData;
 }
 
+// Panel geometry (relative to the artboard). Kept as a constant so the click
+// backdrop can align its top edge to the panel — the backdrop starts BELOW the
+// TopNav so the top tabs stay clickable while an overlay is open.
+const PANEL_TOP = 80;
+
 export default function SectionOverlay({
   active,
   onClose,
@@ -105,6 +110,28 @@ export default function SectionOverlay({
   }, []);
 
   return (
+    <>
+      {/* Click-outside backdrop. A transparent layer covering the artboard BELOW
+          the TopNav (top: PANEL_TOP) — clicking the margin area around the panel
+          closes the overlay (in addition to Esc). It is a SIBLING of the dialog
+          (not an ancestor) and sits one z-index below it, so clicks inside the
+          panel / on its buttons never reach this handler (they don't bubble to a
+          sibling) and therefore never close the overlay. Starting below the nav
+          keeps the top tabs clickable. aria-hidden + no tabIndex → invisible to
+          AT and keyboard; Esc remains the keyboard close path. */}
+      <div
+        aria-hidden="true"
+        onClick={onClose}
+        style={{
+          position: "absolute",
+          left: 0,
+          right: 0,
+          top: PANEL_TOP,
+          bottom: 0,
+          zIndex: 29,
+        }}
+      />
+
       <div
         ref={dialogRef}
         role="dialog"
@@ -115,7 +142,7 @@ export default function SectionOverlay({
           position: "absolute",
           left: 28,
           right: 28,
-        top: 80,
+          top: PANEL_TOP,
           bottom: 30,
           zIndex: 30,
           display: "flex",
@@ -131,8 +158,19 @@ export default function SectionOverlay({
         }}
       >
         <style>{`
-        .tiv2-so-back { color: ${tokens.ink}; transition: all .15s; }
-        .tiv2-so-back:hover { border-color: ${tokens.accent}; color: ${tokens.accent}; }
+          .tiv2-so-back {
+            transition: all .15s;
+            background: ${tokens.accentDeep};
+            box-shadow: 0 3px 10px rgba(46,139,255,.28);
+          }
+          .tiv2-so-back:hover {
+            box-shadow: 0 6px 16px rgba(46,139,255,.45);
+            transform: translateY(-1px);
+          }
+          .tiv2-so-back:active {
+            transform: translateY(0);
+            box-shadow: 0 2px 6px rgba(46,139,255,.3);
+          }
         `}</style>
 
         {/* HUD corner brackets */}
@@ -198,23 +236,33 @@ export default function SectionOverlay({
             type="button"
             onClick={onClose}
             className="tiv2-so-back"
+            aria-label="Вернуться к оценке"
             style={{
               display: "flex",
               alignItems: "center",
               gap: 8,
               cursor: "pointer",
-            border: `1px solid ${tokens.line}`,
+              border: `1px solid ${tokens.accentDeep}`,
               borderRadius: 6,
-            padding: "6px 12px",
-            background: tokens.surface.w60,
-            // reset UA button defaults while keeping the original box look;
-            // base colour lives in .tiv2-so-back so :hover can win
+              padding: "8px 15px",
+              // background + shadow live in .tiv2-so-back so :hover can override
+              // them (an inline background would beat the hover rule on
+              // specificity). Solid accentDeep keeps white text ≥4.5:1 (AA).
               fontFamily: "inherit",
             }}
           >
-          <span style={{ fontSize: 13 }}>←</span>
             <span
-            style={{ fontSize: 10, letterSpacing: 1.5, color: tokens.body2 }}
+              style={{ fontSize: 15, color: tokens.onAccent, lineHeight: 1 }}
+            >
+              ←
+            </span>
+            <span
+              style={{
+                fontSize: 11,
+                fontWeight: 600,
+                letterSpacing: 1.5,
+                color: tokens.onAccent,
+              }}
             >
               К ОЦЕНКЕ
             </span>
@@ -238,5 +286,6 @@ export default function SectionOverlay({
           {active === 4 && <CacheView data={cache} />}
         </div>
       </div>
+    </>
   );
 }