feat(changelog): surface release notes from sidebar menu + update prompt

Two entry points to multica.ai/changelog so users actually find out
what shipped:

- Sidebar user menu (both expanded popover + collapsed dropdown
  variants) gains a "What's new" item with a Sparkles icon, sitting
  above Log out. Plain `<a target="_blank">` works on both surfaces:
  web opens a new tab, desktop's main-process
  setWindowOpenHandler intercepts and routes through
  openExternalSafely. The shared view doesn't need to branch.
- Desktop's UpdateNotification "ready to restart" card grows a
  secondary "See changes" button next to "Restart now", giving the
  user a reason to actually restart instead of dismissing. Mirrors
  Conductor's update prompt pattern. The "available" / "downloading"
  states stay action-only — the changelog isn't useful before the
  download finishes.

No version-detection / unread-tracking yet. Web users still need to
click into the menu to see the changelog; that's a follow-up if the
team wants Linear-style "new" dot.

apps/desktop/src/renderer/src/components/update-notification.tsx

@@ -110,12 +110,25 @@ export function UpdateNotification() {
             <p className="text-xs text-muted-foreground mt-0.5">
               Restart to apply the update
             </p>
-            <button
-              onClick={handleInstall}
-              className="mt-2 inline-flex items-center rounded-md bg-primary px-3 py-1.5 text-xs font-medium text-primary-foreground hover:bg-primary/90 transition-colors"
-            >
-              Restart now
-            </button>
+            <div className="mt-2 flex items-center gap-1.5">
+              {/* Secondary "See changes" — gives the user a reason to
+                  restart by surfacing what they're about to get. Opens
+                  in the default browser via the shared openExternal
+                  bridge so the URL hits the same allow-list as every
+                  other outbound link. */}
+              <button
+                onClick={() => window.desktopAPI.openExternal("https://multica.ai/changelog")}
+                className="inline-flex items-center rounded-md border border-border bg-background px-3 py-1.5 text-xs font-medium text-foreground hover:bg-accent transition-colors"
+              >
+                See changes
+              </button>
+              <button
+                onClick={handleInstall}
+                className="inline-flex items-center rounded-md bg-primary px-3 py-1.5 text-xs font-medium text-primary-foreground hover:bg-primary/90 transition-colors"
+              >
+                Restart now
+              </button>
+            </div>
           </div>
         </div>
       )}

packages/views/layout/app-sidebar.tsx

@@ -28,6 +28,7 @@ import {
   SquarePen,
   CircleUser,
   FolderKanban,
+  Sparkles,
   X,
   Zap,
 } from "lucide-react";
@@ -415,6 +416,22 @@ export function AppSidebar({ topSlot, searchSlot, headerClassName, headerStyle }
                   )}
                   <DropdownMenuSeparator />
                   <DropdownMenuGroup>
+                    {/* Plain anchor with target=_blank works on both web
+                        (new tab) and desktop (intercepted by the main
+                        process's setWindowOpenHandler → openExternalSafely),
+                        so the shared component doesn't need to branch. */}
+                    <DropdownMenuItem
+                      render={
+                        <a
+                          href="https://multica.ai/changelog"
+                          target="_blank"
+                          rel="noopener noreferrer"
+                        />
+                      }
+                    >
+                      <Sparkles className="h-3.5 w-3.5" />
+                      What&apos;s new
+                    </DropdownMenuItem>
                     <DropdownMenuItem variant="destructive" onClick={logout}>
                       <LogOut className="h-3.5 w-3.5" />
                       Log out
@@ -599,6 +616,15 @@ export function AppSidebar({ topSlot, searchSlot, headerClassName, headerStyle }
                   </div>
                 </div>
                 <div className="p-1">
+                  <a
+                    href="https://multica.ai/changelog"
+                    target="_blank"
+                    rel="noopener noreferrer"
+                    className="flex w-full items-center gap-2 rounded-md px-2 py-1.5 text-sm text-foreground hover:bg-accent transition-colors cursor-pointer"
+                  >
+                    <Sparkles className="h-3.5 w-3.5" />
+                    What&apos;s new
+                  </a>
                   <button
                     onClick={logout}
                     className="flex w-full items-center gap-2 rounded-md px-2 py-1.5 text-sm text-destructive hover:bg-destructive/10 transition-colors cursor-pointer"