Remove legacy absolute positioning from nav buttons

The #depsBtn and #helpBtn had old right positioning rules
that conflicted with the flex layout, causing them to appear
in wrong positions.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

static/css/index.css

@@ -1025,13 +1025,6 @@ header h1 .tagline {
     background: var(--bg-secondary);
 }
 
-#depsBtn {
-    right: 5.5em;
-}
-
-#helpBtn {
-    right: 3.5em;
-}
 
 .theme-toggle {
     position: absolute;