feat(journey): combined map+timeline view on mobile (Polarsteps-style)

Merge the separate Timeline and Map tabs into a single fullscreen
combined view on mobile (<1024px). A Leaflet map fills the background
while a horizontal snap-scroll carousel of entry cards sits at the
bottom. Scrolling the carousel auto-focuses the corresponding map
marker; tapping a marker scrolls to the card. Tapping a card opens
a new fullscreen entry view with edit/delete actions.

- New: MobileMapTimeline, MobileEntryCard, MobileEntryView components
- New: useIsMobile hook (matchMedia < 1024px)
- JourneyMap: fullScreen + paddingBottom props, focusMarker guard
- Desktop layout completely unchanged
- Public share page gets the same combined view (read-only)
- Fix: entry editor now portaled to body (iOS stacking context)
- Fix: pros/cons dark mode input backgrounds
- Fix: mood button borders in dark mode
- Fix: location icon color (neutral instead of green/indigo)

client/src/hooks/useIsMobile.ts

@@ -0,0 +1,18 @@
+import { useState, useEffect } from 'react'
+
+/** Returns true when the viewport is below the lg breakpoint (1024px). */
+export function useIsMobile(): boolean {
+  const [isMobile, setIsMobile] = useState(
+    () => typeof window !== 'undefined' && window.innerWidth < 1024,
+  )
+
+  useEffect(() => {
+    const mq = window.matchMedia('(max-width: 1023px)')
+    const handler = (e: MediaQueryListEvent) => setIsMobile(e.matches)
+    setIsMobile(mq.matches)
+    mq.addEventListener('change', handler)
+    return () => mq.removeEventListener('change', handler)
+  }, [])
+
+  return isMobile
+}