fix(sidebar): lock user menu position when sidebar is resized (#21853)

Use align="start" (left-anchor) instead of align="end" (right-anchor) on
the user menu DropdownMenu.Content, combined with avoidCollisions={false}
to prevent Floating UI from auto-flipping back to end-alignment when the
menu's left edge is near the viewport boundary.

Previously, the right edge of the full-width trigger row tracked the
right edge of the sidebar, so resizing the sidebar wider caused the menu
to drift rightward. With start alignment the menu is anchored to the
left edge of the trigger, which is stable regardless of sidebar width.

src/lib/components/layout/Sidebar/UserMenu.svelte

@@ -88,7 +88,8 @@
 			class="w-full {className}  rounded-2xl px-1 py-1  border border-gray-100  dark:border-gray-800 z-50 bg-white dark:bg-gray-850 dark:text-white shadow-lg text-sm"
 			sideOffset={4}
 			side="top"
-			align="end"
+			align="start"
+			avoidCollisions={false}
 			transition={(e) => fade(e, { duration: 100 })}
 		>
 			{#if profile}