redesign: YearSelector as a compact dropdown next to MonthSelector

The pill-row year switcher from the previous commit added a whole
extra row of buttons above the month pills, which read as cluttered.
Replaced it with a single dropdown button (current year + chevron)
placed to the right of MonthSelector on all three pages, matching how
a lot of finance-app date pickers separate month (frequent) from year
(occasional) navigation.

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "aurum-frontend",
   "private": true,
-  "version": "0.16.0",
+  "version": "0.16.1",
   "type": "module",
   "scripts": {
     "dev": "vite",