feat(nav): mobile bottom tab bar and ≥44px logo tap target

MOB-01: At ≤640px the top inline nav is hidden and replaced by a
fixed bottom tab bar (Search / Compare / Rankings / Admissions) with
icon + label, 56px tap targets, env(safe-area-inset-bottom) padding,
and the Compare count rendered as a badge on the icon. Eliminates
horizontal page overflow on every route (docW was 401–429 at vw 390;
now docW === vw).

MOB-02: Logo link gains a padded hit area so the touch target is
≥44×44 (was 36×36), without resizing the visual mark.

ComparisonToast lifted above the new bottom bar on mobile so the two
do not stack on top of each other. body gets a bottom padding equal
to the bar height + safe-area inset so page content is never hidden.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

nextjs-app/components/Navigation.module.css

@@ -21,11 +21,15 @@
   display: flex;
   align-items: center;
   gap: 0.75rem;
+  /* Padded hit area so the logo link is ≥44×44 on touch */
+  margin: -0.375rem -0.5rem;
+  padding: 0.375rem 0.5rem;
   text-decoration: none;
   color: var(--text-primary, #1a1612);
   font-size: 1.25rem;
   font-weight: 700;
   transition: color 0.2s ease;
+  -webkit-tap-highlight-color: transparent;
 }
 
 .logo:hover {
@@ -33,11 +37,17 @@
 }
 
 .logoIcon {
+  display: inline-flex;
   width: 36px;
   height: 36px;
   color: var(--accent-coral, #e07256);
 }
 
+.logoIcon svg {
+  width: 100%;
+  height: 100%;
+}
+
 .logoText {
   font-family: var(--font-playfair), 'Playfair Display', serif;
   font-weight: 700;
@@ -126,21 +136,102 @@
   }
 }
 
+/* ─── Bottom tab bar (mobile only) ──────────────────────────────── */
+
+.bottomBar {
+  display: none;
+}
+
+.tab {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  gap: 0.2rem;
+  flex: 1;
+  min-height: 56px;
+  padding: 0.375rem 0.25rem;
+  color: var(--text-secondary, #5c564d);
+  text-decoration: none;
+  font-size: 0.6875rem;
+  font-weight: 500;
+  letter-spacing: 0.01em;
+  transition: color 0.15s ease, background-color 0.15s ease;
+  -webkit-tap-highlight-color: transparent;
+}
+
+.tab:active {
+  background: var(--bg-secondary, #f3ede4);
+}
+
+.tabActive {
+  color: var(--accent-coral, #e07256);
+}
+
+.tabIconWrap {
+  position: relative;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: 24px;
+  height: 24px;
+}
+
+.tabIcon {
+  width: 22px;
+  height: 22px;
+}
+
+.tabLabel {
+  line-height: 1;
+}
+
+.tabBadge {
+  position: absolute;
+  top: -6px;
+  right: -10px;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-width: 18px;
+  height: 18px;
+  padding: 0 5px;
+  font-size: 0.6875rem;
+  font-weight: 700;
+  color: white;
+  background: var(--accent-coral, #e07256);
+  border: 2px solid var(--bg-card, white);
+  border-radius: 9999px;
+  animation: badgePop 0.3s ease-out;
+}
+
 @media (max-width: 640px) {
   .container {
     padding: 0 1rem;
+    height: 56px;
   }
 
-  .logoText {
+  /* Hide the top text nav; the bottom bar takes over */
+  .nav {
     display: none;
   }
 
-  .nav {
-    gap: 0.25rem;
+  .logoIcon {
+    width: 32px;
+    height: 32px;
   }
 
-  .navLink {
-    padding: 0.5rem 0.75rem;
-    font-size: 0.875rem;
+  .bottomBar {
+    display: flex;
+    position: fixed;
+    bottom: 0;
+    left: 0;
+    right: 0;
+    z-index: 1000;
+    background: var(--bg-card, white);
+    border-top: 1px solid var(--border-color, #e5dfd5);
+    box-shadow: 0 -2px 12px rgba(26, 22, 18, 0.06);
+    /* Respect iPhone home-indicator inset */
+    padding-bottom: env(safe-area-inset-bottom, 0);
   }
 }