fix(ui): keep close button in flow, fix user section indentation

- Close button: use align-self: flex-end with negative margins instead
  of absolute positioning (which overlapped first two nav items)
- User panel: reset full padding (not just padding-inline) on mobile
  to eliminate inherited desktop spacing
- Settings link and signout button: zero out padding-inline on mobile
  so text aligns with nav links and divider lines

Author: danielnaab

src/design-system/components/flex-header/styles.css

@@ -364,9 +364,8 @@ flex-header {
 
   .flex-header__close-btn {
     display: block;
-    position: absolute;
-    inset-block-start: 0.25rem;
-    inset-inline-end: 0.25rem;
+    align-self: flex-end;
+    margin: -0.5rem -0.5rem 0;
   }
 
   .flex-header__nav-list {
@@ -424,19 +423,28 @@ flex-header {
   }
 
   .flex-header__user-identity {
-    padding-inline: 0;
+    padding: 0;
   }
 
   .flex-header__user-theme {
-    padding-inline: 0;
+    padding: 0;
   }
 
   .flex-header__user-settings {
+    padding: 0;
+  }
+
+  .flex-header__user-settings-link {
     padding-inline: 0;
   }
 
   .flex-header__user-signout {
+    padding: 0;
+  }
+
+  .flex-header__user-signout-btn {
     padding-inline: 0;
+    text-align: start;
   }
 
   /* Signed-out parallel: theme toggle as a utility section at the bottom of the panel */