feat(web): use company logo PNG in brand mark

Replace the JC text mark in AppShell and login with the real
company_logo.png. Restyle .brand-mark to host the image (white
rounded bg, object-fit contain). Appbar 38px, login panel 46px.

apps/web/src/app/globals.css

@@ -200,19 +200,20 @@ button {
   text-decoration: none;
 }
 .brand-mark {
-  width: 34px;
-  height: 34px;
+  width: 38px;
+  height: 38px;
   border-radius: 9px;
-  background: radial-gradient(circle at 30% 25%, var(--brand-500), var(--brand-700));
+  background: #fbf8f0;
   border: 1px solid rgba(255, 255, 255, 0.18);
-  display: grid;
-  place-items: center;
-  font-family: var(--font-display);
-  font-weight: 600;
-  font-size: 16px;
-  color: #f5efe0;
+  object-fit: contain;
+  padding: 3px;
   box-shadow: inset 0 1px 1px rgba(255, 255, 255, 0.2);
 }
+.login-brand .brand-mark {
+  width: 46px;
+  height: 46px;
+  border-radius: 10px;
+}
 .brand-text {
   display: flex;
   flex-direction: column;