Fix historical chart y-axis to use evenly spaced ticks

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: DTrim99

frontend/components/PolicyOverview.tsx

@@ -91,7 +91,7 @@ export default function PolicyOverview() {
             <BarChart data={KICKER_HISTORY} margin={{ top: 10, right: 30, left: 20, bottom: 5 }}>
               <CartesianGrid strokeDasharray="3 3" vertical={false} />
               <XAxis dataKey="year" tick={{ fontSize: 12 }} />
-              <YAxis tickFormatter={(v) => `${(v * 100).toFixed(0)}%`} tick={{ fontSize: 12 }} domain={[0, 0.5]} />
+              <YAxis tickFormatter={(v) => `${(v * 100).toFixed(0)}%`} tick={{ fontSize: 12 }} domain={[0, 0.5]} ticks={[0, 0.1, 0.2, 0.3, 0.4, 0.5]} />
               <Tooltip
                 content={({ active, payload, label }) => {
                   if (!active || !payload?.length) return null;