ui: add animations to properties panel toggle

- Move toggle icon next to three-dots menu in a shared flex container
- Toggle icon fades in/out with opacity transition instead of hard mount/unmount
- Properties panel slides in/out with width + opacity transition (200ms ease-in-out)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/components/PropertiesPanel.tsx

@@ -6,19 +6,24 @@ import { ScrollArea } from "@/components/ui/scroll-area";
 export function PropertiesPanel() {
   const { panelContent, panelVisible, setPanelVisible } = usePanel();
 
-  if (!panelContent || !panelVisible) return null;
+  if (!panelContent) return null;
 
   return (
-    <aside className="hidden md:flex w-80 border-l border-border bg-card flex-col shrink-0">
-      <div className="flex items-center justify-between px-4 py-2 border-b border-border">
-        <span className="text-sm font-medium">Properties</span>
-        <Button variant="ghost" size="icon-xs" onClick={() => setPanelVisible(false)}>
-          <X className="h-4 w-4" />
-        </Button>
+    <aside
+      className="hidden md:flex border-l border-border bg-card flex-col shrink-0 overflow-hidden transition-[width,opacity] duration-200 ease-in-out"
+      style={{ width: panelVisible ? 320 : 0, opacity: panelVisible ? 1 : 0 }}
+    >
+      <div className="w-80 flex-1 flex flex-col min-w-[320px]">
+        <div className="flex items-center justify-between px-4 py-2 border-b border-border">
+          <span className="text-sm font-medium">Properties</span>
+          <Button variant="ghost" size="icon-xs" onClick={() => setPanelVisible(false)}>
+            <X className="h-4 w-4" />
+          </Button>
+        </div>
+        <ScrollArea className="flex-1">
+          <div className="p-4">{panelContent}</div>
+        </ScrollArea>
       </div>
-      <ScrollArea className="flex-1">
-        <div className="p-4">{panelContent}</div>
-      </ScrollArea>
     </aside>
   );
 }

ui/src/pages/IssueDetail.tsx

@@ -613,24 +613,26 @@ export function IssueDetail() {
             <SlidersHorizontal className="h-4 w-4" />
           </Button>
 
-          {!panelVisible && (
+          <div className="hidden md:flex items-center md:ml-auto shrink-0">
             <Button
               variant="ghost"
               size="icon-xs"
-              className="hidden md:inline-flex ml-auto shrink-0"
+              className={cn(
+                "shrink-0 transition-opacity duration-200",
+                panelVisible ? "opacity-0 pointer-events-none w-0 overflow-hidden" : "opacity-100",
+              )}
               onClick={() => setPanelVisible(true)}
               title="Show properties"
             >
               <SlidersHorizontal className="h-4 w-4" />
             </Button>
-          )}
 
-          <Popover open={moreOpen} onOpenChange={setMoreOpen}>
-            <PopoverTrigger asChild>
-              <Button variant="ghost" size="icon-xs" className="md:ml-auto shrink-0">
-                <MoreHorizontal className="h-4 w-4" />
-              </Button>
-            </PopoverTrigger>
+            <Popover open={moreOpen} onOpenChange={setMoreOpen}>
+              <PopoverTrigger asChild>
+                <Button variant="ghost" size="icon-xs" className="shrink-0">
+                  <MoreHorizontal className="h-4 w-4" />
+                </Button>
+              </PopoverTrigger>
             <PopoverContent className="w-44 p-1" align="end">
               <button
                 className="flex items-center gap-2 w-full px-2 py-1.5 text-xs rounded hover:bg-accent/50 text-destructive"
@@ -646,7 +648,8 @@ export function IssueDetail() {
                 Hide this Issue
               </button>
             </PopoverContent>
-          </Popover>
+            </Popover>
+          </div>
         </div>
 
         <InlineEditor