add tangled to right sidebar

web/src/components/navigation/RightSidebar.tsx

···
               Terms
             </a>
             <a
-              href="https://github.com/margin-at"
+              href="https://github.com/margin-at/margin"
               target="_blank"
               rel="noreferrer"
               className="hover:underline hover:text-surface-600 dark:hover:text-surface-300"
             >
-              Code
+              GitHub
+            </a>
+            <a
+              href="https://tangled.org/margin.at/margin"
+              target="_blank"
+              rel="noreferrer"
+              className="hover:underline hover:text-surface-600 dark:hover:text-surface-300"
+            >
+              Tangled
             </a>
             <span>© 2026 Margin</span>
           </div>

web/src/views/core/Feed.tsx

···
             </Button>
             <Button
               variant="secondary"
-              onClick={() =>
-                window.open("https://github.com/margin-at", "_blank")
-              }
+              onClick={() => window.open("/about", "_blank")}
             >
               Learn More
             </Button>