Add responsive app shell, routes and navigation

Replace the catch-all placeholder with an AppShell that renders one
primary nav per breakpoint (chosen with matchMedia via useBreakpoint):
a dark pill bottom bar below 768 px, a 96 px rail with the "M" mark at
768-1199 px, and a 208 px sidebar with the MealQuest wordmark and the
"Our kitchen / Shared household" card at 1200 px and up. Nav order is
Home, Plan, Discover, Quick, Settings; NavLink marks the active item
aria-current="page", with nested Plan and Settings paths keeping their
parent current. The mobile scroll area reserves 100 px plus the safe
area beneath its content.

Register every handoff route plus /settings/household,
/settings/regulars and /settings/calendar, each with a placeholder
heading. Remove the default body margin so the shell fills the viewport.

Tests force each breakpoint with a matchMedia mock and assert the
routes, nav order, each layout's structure, aria-current and the
mobile bottom padding from the stylesheet.

Maestro task: 42a4695a-6bd0-49a1-925e-387858dbee48

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/shell/BottomBar.tsx

@@ -0,0 +1,23 @@
+import { NavLink } from 'react-router'
+import { Icon } from '../ui/Icon.tsx'
+import { navItems } from './navItems.ts'
+import styles from './BottomBar.module.css'
+
+// Mobile nav: a dark pill bar floating over the bottom of the screen. Inactive
+// items show only their icon; the active item adds its label on a grape pill.
+export function BottomBar() {
+  return (
+    <nav aria-label="Primary" className={styles.bar}>
+      {navItems.map((item) => (
+        <NavLink key={item.to} to={item.to} end={item.end} className={styles.item}>
+          {({ isActive }) => (
+            <span className={isActive ? `${styles.pill} ${styles.active}` : styles.pill}>
+              <Icon icon={item.icon} size="nav" />
+              <span className={isActive ? styles.label : styles.hiddenLabel}>{item.label}</span>
+            </span>
+          )}
+        </NavLink>
+      ))}
+    </nav>
+  )
+}