Fix hole-punch regressions: transparency chain, black backing, keyboard

Three fixes for the hole-punch build:
1. White background + shared screen not showing: body and .content both use
   var(--bg) (a light colour) and were still opaque, occluding the native
   video behind the WebView. Make the WHOLE meeting chain transparent under
   .bz-hp (body + .content, on top of .meet-grid/tiles).
2. Backing: also set the view controller's view background to black (saved/
   restored) so any transparent gap reads black, not white — belt-and-braces
   with webView.backgroundColor.
3. Keyboard covering the in-call chat: keyboard resize is "none", so the
   absolutely-positioned meet panels don't move for the keyboard. Lift
   .meet-panel by the reported keyboard height (body.kb-open → bottom:
   calc(var(--kb)+12px)); --kb/kb-open are already set globally by the
   Keyboard listener.

Plugin change (VC background) needs a build; the CSS is web-deployed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

mobile/plugins/native-call/ios/Sources/NativeCallPlugin/NativeCallPlugin.swift

@@ -58,6 +58,7 @@ public class NativeCallPlugin: CAPPlugin, CAPBridgedPlugin, PKPushRegistryDelega
     private var savedWebOpaque = true
     private var savedWebBg: UIColor?
     private var savedScrollBg: UIColor?
+    private var savedVCBg: UIColor?
 
     override public func load() {
         let config = CXProviderConfiguration(localizedName: "Biz Connect")
@@ -197,10 +198,12 @@ public class NativeCallPlugin: CAPPlugin, CAPBridgedPlugin, PKPushRegistryDelega
                     self.savedWebOpaque = web.isOpaque
                     self.savedWebBg = web.backgroundColor
                     self.savedScrollBg = web.scrollView.backgroundColor
+                    self.savedVCBg = self.bridge?.viewController?.view.backgroundColor
                 }
                 web.isOpaque = false
                 web.backgroundColor = .black          // shows through the transparent meeting; also the letterbox bg
                 web.scrollView.backgroundColor = .clear
+                self.bridge?.viewController?.view.backgroundColor = .black // backing so the transparent meeting reads black, not white
                 self.holePunchOn = true
             } else {
                 self.applyHolePunchRestore(web)
@@ -217,6 +220,7 @@ public class NativeCallPlugin: CAPPlugin, CAPBridgedPlugin, PKPushRegistryDelega
         web.isOpaque = savedWebOpaque
         web.backgroundColor = savedWebBg
         web.scrollView.backgroundColor = savedScrollBg
+        bridge?.viewController?.view.backgroundColor = savedVCBg
         holePunchOn = false
     }