perf: major trip planner performance overhaul (#218)

Store & re-render optimization:
- TripPlannerPage uses selective Zustand selectors instead of full store
- placesSlice only updates affected days on place update/delete
- Route calculation only reacts to selected day's assignments
- DayPlanSidebar uses stable action refs instead of full store

Map marker performance:
- Shared photoService for PlaceAvatar and MapView (single cache, no duplicate requests)
- Client-side base64 thumbnail generation via canvas (CORS-safe for Wikimedia)
- Map markers use base64 data URL <img> tags for smooth zoom (no external image decode)
- Sidebar uses same base64 thumbnails with IntersectionObserver for visible-first loading
- Icon cache prevents duplicate L.divIcon creation
- MarkerClusterGroup with animate:false and optimized chunk settings
- Photo fetch deduplication and batched state updates

Server optimizations:
- Wikimedia image size reduced to 400px (from 600px)
- Photo cache: 5min TTL for errors (was 12h), prevents stale 404 caching
- Removed unused image-proxy endpoint

UX improvements:
- Splash screen with plane animation during initial photo preload
- Markdown rendering in DayPlanSidebar place descriptions
- Missing i18n keys added, all 12 languages synced to 1376 keys

server/src/routes/maps.ts

@@ -154,7 +154,7 @@ async function fetchWikimediaPhoto(lat: number, lng: number, name?: string): Pro
     ggslimit: '5',
     prop: 'imageinfo',
     iiprop: 'url|extmetadata|mime',
-    iiurlwidth: '600',
+    iiurlwidth: '400',
   });
   try {
     const res = await fetch(`https://commons.wikimedia.org/w/api.php?${params}`, { headers: { 'User-Agent': UA } });
@@ -380,11 +380,14 @@ router.get('/place-photo/:placeId', authenticate, async (req: Request, res: Resp
   const { placeId } = req.params;
 
   const cached = photoCache.get(placeId);
-  if (cached && Date.now() - cached.fetchedAt < PHOTO_TTL) {
-    if (cached.error) {
-      return res.status(404).json({ error: `(Cache) No photo available` });
+  const ERROR_TTL = 5 * 60 * 1000; // 5 min for errors
+  if (cached) {
+    const ttl = cached.error ? ERROR_TTL : PHOTO_TTL;
+    if (Date.now() - cached.fetchedAt < ttl) {
+      if (cached.error) return res.status(404).json({ error: `(Cache) No photo available` });
+      return res.json({ photoUrl: cached.photoUrl, attribution: cached.attribution });
     }
-    return res.json({ photoUrl: cached.photoUrl, attribution: cached.attribution });
+    photoCache.delete(placeId);
   }
 
   // Wikimedia Commons fallback for OSM places (using lat/lng query params)
@@ -436,7 +439,7 @@ router.get('/place-photo/:placeId', authenticate, async (req: Request, res: Resp
     const attribution = photo.authorAttributions?.[0]?.displayName || null;
 
     const mediaRes = await fetch(
-      `https://places.googleapis.com/v1/${photoName}/media?maxHeightPx=600&skipHttpRedirect=true`,
+      `https://places.googleapis.com/v1/${photoName}/media?maxHeightPx=400&skipHttpRedirect=true`,
       { headers: { 'X-Goog-Api-Key': apiKey } }
     );
     const mediaData = await mediaRes.json() as { photoUri?: string };