fix(mobile): keep Android content clear of the navigation bar

Android 15+ enforces edge-to-edge, and Capacitor stops padding the WebView
once it can hand the insets to the page instead — so the app draws under
the gesture/navigation bar. Only the top inset was ever consumed: full
cover surfaces ignored the bottom one entirely, which is why a settings
list ran under the bar, and the chat shell reserved half of it, which is
enough for a home indicator but not for a bar that swallows taps.

Reserve the full inset in the shell on Android and give the surfaces that
own the bottom edge — fullscreen surfaces, the workspace drawer, bottom
sheets — an opt-in class that pads them. The sessions drawer already did
this through its footer, so it stays as it is. Capacitor reports a zero
bottom inset while the keyboard is up, so none of this stacks with the
keyboard inset. iOS deliberately keeps its softer visual inset.

Testing: package type-check and lint; drove the mobile surface in a
browser with the Android platform class and a simulated 48px inset (shell
and surfaces reserve exactly that, drawer footer unchanged, and removing
the class returns every surface to zero).

packages/ui/src/apps/MobileFullscreenSurface.tsx

@@ -175,7 +175,7 @@ export const MobileFullscreenSurface: React.FC<MobileFullscreenSurfaceProps> = (
         'flex flex-col bg-background text-foreground',
         isDialog
           ? 'h-[min(88dvh,860px)] w-full max-w-[720px] overflow-hidden rounded-2xl border border-border/70 shadow-[0_24px_64px_rgb(0_0_0_/_0.32)]'
-          : 'oc-keyboard-inset-surface fixed inset-0 z-50',
+          : 'oc-keyboard-inset-surface oc-bottom-safe-surface fixed inset-0 z-50',
       )}
       style={isDialog ? {
         // Scale/fade instead of the push slide: the card is not a navigation
@@ -249,7 +249,7 @@ export const MobileFullscreenSurface: React.FC<MobileFullscreenSurfaceProps> = (
 
   return createPortal(
     <div
-      className="oc-keyboard-inset-surface fixed inset-0 z-50 flex items-center justify-center p-4 transition-opacity duration-200 ease-out"
+      className="oc-keyboard-inset-surface oc-bottom-safe-surface fixed inset-0 z-50 flex items-center justify-center p-4 transition-opacity duration-200 ease-out"
       style={{
         background: 'rgb(0 0 0 / 0.45)',
         opacity: entered ? 1 : 0,

packages/ui/src/apps/MobileWorkspaceDrawer.tsx

@@ -295,7 +295,7 @@ export const MobileWorkspaceDrawer: React.FC<{
       aria-modal="true"
       aria-label={t('mobile.header.openWorkspaceAria')}
       aria-hidden={!open}
-      className="oc-keyboard-inset-surface fixed inset-0 z-50 flex flex-col bg-background text-foreground"
+      className="oc-keyboard-inset-surface oc-bottom-safe-surface fixed inset-0 z-50 flex flex-col bg-background text-foreground"
       style={{
         paddingTop: 'var(--oc-safe-area-top, 0px)',
         // Settled state drops the transform entirely so the drawer isn't kept