Sheet peek/expand, theme-aware media stage, and edge-to-edge viewer bars

Long-content bottom sheets (Details' Versions/Activity tabs with many
rows) opened locked to nearly full screen height with no room left to
adjust. showNooSheet now measures its content once against the
available height: anything that fits comfortably still sizes to
content as before, but content tall enough to need scrolling opens at
a native-style draggable peek instead, which the user can drag up to
reveal more of (and drag back down to dismiss).

The media viewer's stage was pinned to black regardless of theme,
which read as jarringly out of place in light mode - it now follows
the app's own `bg`. The floating top/bottom bars stay a fixed dark
panel either way (they need to read over arbitrary photo/video
brightness, not over the stage), but both had their SafeArea nested
the wrong way around: it wrapped the whole panel instead of just its
content, so the panel's background stopped short of the actual screen
edge - most visibly the bottom bar ending above the gesture area
instead of extending behind it. The background now wraps the SafeArea
instead.

lib/widgets/viewer/media_action_bar.dart

@@ -46,9 +46,14 @@ class MediaActionBar extends StatelessWidget {
     // favorite/delete stay legible even when the ambient theme is light.
     const dark = NooColors.dark;
 
-    return SafeArea(
-      top: false,
-      child: FrostedGlassContainer(
+    // The blurred/tinted background lives outside the SafeArea (not inside
+    // it) so it extends all the way to the physical bottom edge, behind the
+    // gesture bar/home indicator, instead of the panel itself stopping
+    // short and leaving that strip unstyled - only the actual row content
+    // needs padding up and away from the gesture area.
+    return FrostedGlassContainer(
+      child: SafeArea(
+        top: false,
         child: Column(
           mainAxisSize: MainAxisSize.min,
           children: [