Use three-year model (unified_m3_mod) to fetch observed data for all waves

One-year models don't return historical arrest data; three-year models
include observed counts across all CRDC waves (15-16, 17-18, 21-22).

src/components/ChartPanel.jsx

@@ -28,11 +28,12 @@ export default function ChartPanel({ district, state }) {
         }
         setNationalRates(nat)
 
-        // Fetch all 3 waves × default model (unified_m2_mod) for Chart 1 + Charts 2-3
+        // Fetch all 3 waves × three-year model (unified_m3_mod) for Chart 1 + Charts 2-3
+        // Three-year models return observed data for all waves
         const waves = ['21-22', '17-18', '15-16']
         const waveData = {}
         await Promise.all(waves.map(async (year) => {
-          try { waveData[year] = await api.fetchDistrictEstimates(district.leaid, { model: 'unified_m2_mod', year }) } catch(e) {} 
+          try { waveData[year] = await api.fetchDistrictEstimates(district.leaid, { model: 'unified_m3_mod', year }) } catch(e) {} 
         }))
 
         // Fetch all 4 quadrant models for Charts 4-6 (8 groups × 4 models, but we batch by model)