Style nav links as buttons across all three pages

Replace plain text/opacity links with bordered pill buttons that fill
with accent color on hover — consistent across main app, conditions,
and dashboard headers.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/public/conditions.html

@@ -74,15 +74,23 @@ html, body {
   display: inline-flex;
   align-items: center;
   gap: 0.2rem;
-  font-size: 0.8rem;
+  font-size: 0.78rem;
   font-weight: 600;
   letter-spacing: 0.04em;
-  color: var(--accent);
+  color: var(--muted);
   text-decoration: none;
   white-space: nowrap;
-  transition: opacity .15s;
+  padding: 0.32rem 0.75rem;
+  border: 1px solid var(--border);
+  border-radius: 8px;
+  background: transparent;
+  transition: background .15s, border-color .15s, color .15s;
+}
+.hdr-back:hover {
+  background: var(--accent);
+  border-color: var(--accent);
+  color: #fff;
 }
-.hdr-back:hover { opacity: .75; }
 .hdr-sep {
   color: var(--border);
   font-size: 0.8rem;
@@ -134,13 +142,20 @@ html, body {
 .hdr-dash-link {
   font-size: 0.78rem;
   font-weight: 600;
-  color: var(--accent);
+  color: var(--muted);
   text-decoration: none;
   white-space: nowrap;
-  opacity: .85;
-  transition: opacity .15s;
+  padding: 0.32rem 0.75rem;
+  border: 1px solid var(--border);
+  border-radius: 8px;
+  background: transparent;
+  transition: background .15s, border-color .15s, color .15s;
+}
+.hdr-dash-link:hover {
+  background: var(--accent);
+  border-color: var(--accent);
+  color: #fff;
 }
-.hdr-dash-link:hover { opacity: 1; }
 
 /* ── Hero ────────────────────────────────────────────────── */
 .hero {