fix(share): anchor SharePopover via documented MudPopover RelativeWidth

Use Fixed + RelativeWidth=Adaptive with BottomLeft/TopLeft origins to
anchor the menu under the share button; drop the inline-block shrink-wrap
container hack. Keep AutoClose off so the embed panel survives clicks.

DeepDrftPublic.Client/Controls/SharePopover.razor

@@ -1,14 +1,17 @@
 @namespace DeepDrftPublic.Client.Controls
 
 @* Overlay is viewport-level/fixed regardless of DOM nesting; placing it outside
-   the wrapper is harmless/cleaner but doesn't change its behavior. *@
-<MudOverlay Visible="@_open" OnClick="@Close" AutoClose="true" />
+   the wrapper is harmless/cleaner but doesn't change its behavior.
+   AutoClose is deliberately OFF: its modeless pointer-down tracking closes the
+   popover on any click outside the overlay's DOM subtree — including the portaled
+   embed checkbox/copy-button — which kills the embed affordance. Backdrop
+   dismissal is handled by OnClick alone. *@
+<MudOverlay Visible="@_open" OnClick="@Close" />
 
-@* display:inline-block is the load-bearing property: it shrink-wraps this div
-   to the button, so MudPopover's portal reads the button's tight bounding rect
-   (via parentNode.getBoundingClientRect()) rather than a page-wide flow box.
-   position:relative is incidental. *@
-<div class="deepdrft-share-popover-anchor">
+@* Activator and popover share this wrapper so MudPopover's anchoring reads the
+   button's bounding rect. No shrink-wrap sizing — width/min-width come from the
+   documented RelativeWidth="Adaptive" on the popover, not from container CSS. *@
+<div>
     <MudTooltip Text="Share">
         <MudIconButton Icon="@Icons.Material.Filled.Share"
                        Size="Size.Large"
@@ -19,9 +22,10 @@
     </MudTooltip>
 
     <MudPopover Open="@_open"
-                Fixed="false"
-                AnchorOrigin="Origin.BottomRight"
-                TransformOrigin="Origin.TopRight"
+                Fixed="true"
+                RelativeWidth="DropdownWidth.Adaptive"
+                AnchorOrigin="Origin.BottomLeft"
+                TransformOrigin="Origin.TopLeft"
                 Class="deepdrft-share-popover">
         <MudStack Spacing="2" Class="deepdrft-share-popover-body">
 

DeepDrftPublic/wwwroot/styles/deepdrft-styles.css

@@ -358,15 +358,6 @@ h2, h3, h4, h5, h6,
     font-family: var(--deepdrft-font-mono) !important;
 }
 
-/* display:inline-block is load-bearing: it shrink-wraps the wrapper to the
-   button so MudPopover's portal reads the button's tight bounding rect
-   (parentNode.getBoundingClientRect()) instead of a page-wide flow box.
-   position:relative is incidental — do not drop inline-block. */
-.deepdrft-share-popover-anchor {
-    position: relative;
-    display: inline-block;
-}
-
 .deepdrft-share-popover-body {
     padding: 0.75rem 1rem;
     min-width: 280px;