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.tsx

@@ -1,6 +1,6 @@
 /**
  * Navigation Component
- * Main navigation header with active link highlighting
+ * Top header nav for desktop; bottom tab bar for mobile (≤640px).
  */
 
 'use client';
@@ -10,63 +10,116 @@ import { usePathname } from 'next/navigation';
 import { useComparison } from '@/hooks/useComparison';
 import styles from './Navigation.module.css';
 
+type IconProps = { className?: string };
+
+const SearchIcon = ({ className }: IconProps) => (
+  <svg className={className} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
+    <circle cx="11" cy="11" r="7" />
+    <path d="m20 20-3.5-3.5" />
+  </svg>
+);
+
+const CompareIcon = ({ className }: IconProps) => (
+  <svg className={className} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
+    <path d="M4 7h13l-3-3" />
+    <path d="M20 17H7l3 3" />
+  </svg>
+);
+
+const RankingsIcon = ({ className }: IconProps) => (
+  <svg className={className} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
+    <path d="M7 21V11" />
+    <path d="M12 21V4" />
+    <path d="M17 21v-7" />
+  </svg>
+);
+
+const AdmissionsIcon = ({ className }: IconProps) => (
+  <svg className={className} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
+    <rect x="3" y="5" width="18" height="16" rx="2" />
+    <path d="M3 10h18M8 3v4M16 3v4" />
+  </svg>
+);
+
 export function Navigation() {
   const pathname = usePathname();
   const { selectedSchools } = useComparison();
 
   const isActive = (path: string) => {
-    if (path === '/') {
-      return pathname === '/';
-    }
+    if (path === '/') return pathname === '/';
     return pathname.startsWith(path);
   };
 
-  return (
-    <header className={styles.header}>
-      <div className={styles.container}>
-        <Link href="/" className={styles.logo}>
-          <div className={styles.logoIcon}>
-            <svg viewBox="0 0 40 40" fill="none" xmlns="http://www.w3.org/2000/svg">
-              <circle cx="20" cy="20" r="18" stroke="currentColor" strokeWidth="2"/>
-              <path d="M20 6L20 34M8 14L32 14M6 20L34 20M8 26L32 26" stroke="currentColor" strokeWidth="1.5" strokeLinecap="round"/>
-              <circle cx="20" cy="20" r="3" fill="currentColor"/>
-            </svg>
-          </div>
-          <span className={styles.logoText}>SchoolCompare</span>
-        </Link>
+  const items = [
+    { href: '/', label: 'Search', Icon: SearchIcon },
+    { href: '/compare', label: 'Compare', Icon: CompareIcon },
+    { href: '/rankings', label: 'Rankings', Icon: RankingsIcon },
+    { href: '/admissions', label: 'Admissions', Icon: AdmissionsIcon },
+  ] as const;
 
-        <nav className={styles.nav} aria-label="Main navigation">
-          <Link
-            href="/"
-            className={isActive('/') ? `${styles.navLink} ${styles.active}` : styles.navLink}
-          >
-            Search
+  return (
+    <>
+      <header className={styles.header}>
+        <div className={styles.container}>
+          <Link href="/" className={styles.logo} aria-label="SchoolCompare home">
+            <span className={styles.logoIcon}>
+              <svg viewBox="0 0 40 40" fill="none" xmlns="http://www.w3.org/2000/svg" aria-hidden="true">
+                <circle cx="20" cy="20" r="18" stroke="currentColor" strokeWidth="2" />
+                <path d="M20 6L20 34M8 14L32 14M6 20L34 20M8 26L32 26" stroke="currentColor" strokeWidth="1.5" strokeLinecap="round" />
+                <circle cx="20" cy="20" r="3" fill="currentColor" />
+              </svg>
+            </span>
+            <span className={styles.logoText}>SchoolCompare</span>
           </Link>
-          <Link
-            href="/compare"
-            className={isActive('/compare') ? `${styles.navLink} ${styles.active}` : styles.navLink}
-          >
-            Compare
-            {selectedSchools.length > 0 && (
-              <span key={selectedSchools.length} className={styles.badge}>
-                {selectedSchools.length}
+
+          <nav className={styles.nav} aria-label="Main navigation">
+            {items.map(({ href, label }) => {
+              const active = isActive(href);
+              const showBadge = href === '/compare' && selectedSchools.length > 0;
+              return (
+                <Link
+                  key={href}
+                  href={href}
+                  className={active ? `${styles.navLink} ${styles.active}` : styles.navLink}
+                  aria-current={active ? 'page' : undefined}
+                >
+                  {label}
+                  {showBadge && (
+                    <span key={selectedSchools.length} className={styles.badge}>
+                      {selectedSchools.length}
+                    </span>
+                  )}
+                </Link>
+              );
+            })}
+          </nav>
+        </div>
+      </header>
+
+      <nav className={styles.bottomBar} aria-label="Main navigation">
+        {items.map(({ href, label, Icon }) => {
+          const active = isActive(href);
+          const showBadge = href === '/compare' && selectedSchools.length > 0;
+          return (
+            <Link
+              key={href}
+              href={href}
+              className={active ? `${styles.tab} ${styles.tabActive}` : styles.tab}
+              aria-current={active ? 'page' : undefined}
+            >
+              <span className={styles.tabIconWrap}>
+                <Icon className={styles.tabIcon} />
+                {showBadge && (
+                  <span key={selectedSchools.length} className={styles.tabBadge} aria-label={`${selectedSchools.length} selected`}>
+                    {selectedSchools.length}
+                  </span>
+                )}
               </span>
-            )}
-          </Link>
-          <Link
-            href="/rankings"
-            className={isActive('/rankings') ? `${styles.navLink} ${styles.active}` : styles.navLink}
-          >
-            Rankings
-          </Link>
-          <Link
-            href="/admissions"
-            className={isActive('/admissions') ? `${styles.navLink} ${styles.active}` : styles.navLink}
-          >
-            Admissions
-          </Link>
-        </nav>
-      </div>
-    </header>
+              <span className={styles.tabLabel}>{label}</span>
+            </Link>
+          );
+        })}
+      </nav>
+    </>
   );
 }