Fix mobile date picker + auto-update end date from start date (v2.3.4)

- Date picker dropdown stays within viewport on mobile (no more overflow)
- Opens above if not enough space below
- Centers on very small screens (<360px)
- End date auto-adjusts when start date changes:
  - If no end date or end < start → end = start
  - If both set → preserves trip duration (shifts end by same delta)

server/package.json

@@ -1,6 +1,6 @@
 {
   "name": "nomad-server",
-  "version": "2.3.3",
+  "version": "2.3.4",
   "main": "src/index.js",
   "scripts": {
     "start": "node --experimental-sqlite src/index.js",