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/src/components/layout/YearSelector.tsx

@@ -1,3 +1,5 @@
+import { useEffect, useRef, useState } from "react";
+import { ChevronDown } from "lucide-react";
 import { cn } from "@/lib/utils";
 
 interface YearSelectorProps {
@@ -6,27 +8,73 @@ interface YearSelectorProps {
   onChange: (year: number) => void;
 }
 
+/** Compact dropdown, most recent year first — sits to the right of
+ * MonthSelector instead of competing with it as a second row of pills. */
 export function YearSelector({ years, year, onChange }: YearSelectorProps) {
+  const [open, setOpen] = useState(false);
+  const rootRef = useRef<HTMLDivElement>(null);
+  const sortedYears = [...years].sort((a, b) => b - a);
+
+  useEffect(() => {
+    if (!open) return;
+    function handlePointerDown(event: MouseEvent) {
+      if (rootRef.current && !rootRef.current.contains(event.target as Node)) {
+        setOpen(false);
+      }
+    }
+    function handleKeyDown(event: KeyboardEvent) {
+      if (event.key === "Escape") setOpen(false);
+    }
+    document.addEventListener("mousedown", handlePointerDown);
+    document.addEventListener("keydown", handleKeyDown);
+    return () => {
+      document.removeEventListener("mousedown", handlePointerDown);
+      document.removeEventListener("keydown", handleKeyDown);
+    };
+  }, [open]);
+
   return (
-    <div className="flex gap-2 overflow-x-auto pb-1 [-ms-overflow-style:none] [scrollbar-width:none] [&::-webkit-scrollbar]:hidden">
-      {years.map((value) => {
-        const active = value === year;
-        return (
-          <button
-            key={value}
-            type="button"
-            onClick={() => onChange(value)}
-            className={cn(
-              "shrink-0 rounded-full border px-3.5 py-1.5 text-sm font-medium transition-colors",
-              active
-                ? "border-text-primary bg-text-primary text-surface-1"
-                : "border-border bg-surface-1 text-text-secondary hover:bg-surface-2"
-            )}
-          >
-            {value}
-          </button>
-        );
-      })}
+    <div ref={rootRef} className="relative shrink-0">
+      <button
+        type="button"
+        onClick={() => setOpen((prev) => !prev)}
+        aria-haspopup="listbox"
+        aria-expanded={open}
+        className="flex h-9 items-center gap-1.5 rounded-lg border border-border bg-surface-1 px-3 text-sm font-medium text-text-primary transition-colors hover:bg-surface-2"
+      >
+        {year}
+        <ChevronDown size={14} className={cn("text-text-muted transition-transform", open && "rotate-180")} />
+      </button>
+
+      {open && (
+        <ul
+          role="listbox"
+          className="absolute right-0 top-full z-20 mt-1.5 max-h-64 w-24 overflow-y-auto rounded-lg border border-border bg-surface-1 py-1 shadow-lg"
+        >
+          {sortedYears.map((value) => {
+            const active = value === year;
+            return (
+              <li key={value}>
+                <button
+                  type="button"
+                  role="option"
+                  aria-selected={active}
+                  onClick={() => {
+                    onChange(value);
+                    setOpen(false);
+                  }}
+                  className={cn(
+                    "block w-full px-3 py-1.5 text-left text-sm transition-colors",
+                    active ? "bg-surface-2 font-semibold text-text-primary" : "text-text-secondary hover:bg-surface-2"
+                  )}
+                >
+                  {value}
+                </button>
+              </li>
+            );
+          })}
+        </ul>
+      )}
     </div>
   );
 }

frontend/src/pages/BudgetPage.tsx

@@ -54,9 +54,11 @@ export function BudgetPage() {
     <div className="space-y-5">
       <AlertBanner />
 
-      <div className="space-y-2">
+      <div className="flex items-center gap-3">
+        <div className="min-w-0 flex-1">
+          <MonthSelector month={month} onChange={setMonth} />
+        </div>
         <YearSelector years={years ?? [now.getFullYear()]} year={year} onChange={setYear} />
-        <MonthSelector month={month} onChange={setMonth} />
       </div>
 
       <Card>

frontend/src/pages/DashboardPage.tsx

@@ -35,9 +35,11 @@ export function DashboardPage() {
     <div className="space-y-5">
       <AlertBanner excludeKeys={["risky_allocation_exceeded"]} />
 
-      <div className="space-y-2">
+      <div className="flex items-center gap-3">
+        <div className="min-w-0 flex-1">
+          <MonthSelector month={month} onChange={setMonth} />
+        </div>
         <YearSelector years={years ?? [now.getFullYear()]} year={year} onChange={setYear} />
-        <MonthSelector month={month} onChange={setMonth} />
       </div>
 
       {isError && (

frontend/src/pages/TransactionsPage.tsx

@@ -63,7 +63,16 @@ export function TransactionsPage() {
   return (
     <div className="space-y-5">
       <div className="flex flex-col gap-3 sm:flex-row sm:items-center sm:justify-between">
-        <div className="space-y-2">
+        <div className="flex min-w-0 flex-1 items-center gap-3">
+          <div className="min-w-0 flex-1">
+            <MonthSelector
+              month={month}
+              onChange={(value) => {
+                setMonth(value);
+                setPage(1);
+              }}
+            />
+          </div>
           <YearSelector
             years={years ?? [now.getFullYear()]}
             year={year}
@@ -72,13 +81,6 @@ export function TransactionsPage() {
               setPage(1);
             }}
           />
-          <MonthSelector
-            month={month}
-            onChange={(value) => {
-              setMonth(value);
-              setPage(1);
-            }}
-          />
         </div>
         <Button onClick={openCreateModal} className="w-full sm:w-auto">
           <Plus size={16} />