Rework corner layout with portrait-style info panel below the video

The corner layout now always renders the info page as a portrait-style
panel below the video (collapsible description, drag to hide/expand),
while the side column holds tabs for the remaining pages. Key pieces:

- Below-video panel reuses PortraitDetailsPanel (no comments pill,
  square corners, chapters/related stay in the side column tabs)
- Drag down hides the panel with the video recentering in lockstep;
  swipe up on the video reveals it following the finger
- Fullscreen button toggles the panels in corner layout (controls hide
  first so their resize never plays visibly); status bar and home
  indicator hide only while the panels are hidden
- Panel visibility and column width are seeded at init from a warmed
  PlayerControlsLayout cache, so the first frame resolves corner mode
  without flashing the default layout or animating the panels in
- Dismiss pan is blocked inside the below-video panel frame
  (cornerBelowPanelFrame in NavigationCoordinator)
- Resize grabber slimmed to match the panel drag handle look

Yattee/Views/Player/ExpandedPlayerWindow.swift

@@ -144,6 +144,8 @@ private final class DragToDismissGestureHandler: NSObject, UIGestureRecognizerDe
     var isPanelDragging: (() -> Bool)?
     /// Returns the portrait panel frame in screen coordinates (for gesture conflict resolution)
     var getPortraitPanelFrame: (() -> CGRect)?
+    /// Returns the corner layout below-video panel frame in screen coordinates (blocks dismiss pan)
+    var getCornerBelowPanelFrame: (() -> CGRect)?
     /// Returns whether the portrait panel is currently visible (not hidden off-screen)
     var isPortraitPanelVisible: (() -> Bool)?
     /// Returns the progress bar frame in screen coordinates (for gesture conflict resolution)
@@ -366,6 +368,16 @@ private final class DragToDismissGestureHandler: NSObject, UIGestureRecognizerDe
             return false
         }
 
+        // Corner layout: don't begin dismiss gesture from inside the
+        // below-video panel — its drag handle hides the panel instead
+        let belowPanelFrame = getCornerBelowPanelFrame?() ?? .zero
+        if !belowPanelFrame.isEmpty {
+            let touchLocation = panGesture.location(in: nil)
+            if belowPanelFrame.contains(touchLocation) {
+                return false
+            }
+        }
+
         // When portrait panel is visible, only allow dismiss from player area (above panel)
         // This prevents race conditions where isPanelDragging isn't set yet when gesture begins
         let panelFrame = getPortraitPanelFrame?() ?? .zero
@@ -845,6 +857,9 @@ final class ExpandedPlayerWindowManager {
         handler.getPortraitPanelFrame = { [weak self] in
             self?.appEnvironment?.navigationCoordinator.portraitPanelFrame ?? .zero
         }
+        handler.getCornerBelowPanelFrame = { [weak self] in
+            self?.appEnvironment?.navigationCoordinator.cornerBelowPanelFrame ?? .zero
+        }
         handler.isPortraitPanelVisible = { [weak self] in
             self?.appEnvironment?.navigationCoordinator.isPortraitPanelVisible ?? true
         }