Question nav + gateway alternatives

- QuestionNav: every other question the visitor currently qualifies
  for, rendered under each page's alternatives - a concern reaches
  the people it speaks to without claiming front-page space, and an
  owner sees the gated desks in the same nav. Context-dependent by
  session (list_qualifying_questions filters via is_qualified).
- An alternative with an action but nothing to submit, confirm, or
  record is a gateway: its button now renders as a real link instead
  of a form submit that did nothing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

style/main.css

@@ -239,6 +239,36 @@ main.not-found {
   }
 }
 
+.question-nav {
+  display: flex;
+  flex-wrap: wrap;
+  justify-content: center;
+  align-items: baseline;
+  gap: 0.5rem 1.2rem;
+  margin: 2.2rem auto 0;
+  max-width: 44rem;
+  padding: 0 1rem;
+  font-size: 0.88rem;
+}
+
+.question-nav-lead {
+  color: var(--ink-dim);
+  text-transform: uppercase;
+  letter-spacing: 0.06em;
+  font-size: 0.72rem;
+}
+
+.question-nav a {
+  color: var(--ink-dim);
+  text-decoration: none;
+  border-bottom: 1px solid var(--line);
+}
+
+.question-nav a:hover {
+  color: var(--accent);
+  border-bottom-color: var(--accent);
+}
+
 .question-responsible {
   text-align: center;
   color: var(--ink-dim);