Couple daily can and spend limits via usual can size

Link daily caps through the user's chosen standard can size (250/355/473ml)
and built-in prices. Onboarding asks for size and can ceiling with derived
spend preview. Settings syncs cans and spend bidirectionally. Forecast lock
button sets both limits together.

Co-authored-by: nh9961 <hello@nedhalksworth.com>

src/App.tsx

@@ -94,6 +94,7 @@ import { createExcelExport, downloadBlob, parseExcelImport } from "./lib/excel";
 import {
   caffeineFor,
   caffeinePerCan,
+  canLimitFromSpend,
   currency,
   currentStreak,
   daysSinceLast,
@@ -656,6 +657,7 @@ function App() {
           onThemeChange={setThemeId}
           onSave={saveOnboarding}
           onClose={() => setSetupOpen(false)}
+          initialLimits={userLimits}
         />
       )}
       <input
@@ -1753,9 +1755,12 @@ function SpendForecastCard({
   const saveLowerLimit = () => {
     if (!onSaveLimits) return;
     const lowerDailyLimit = Math.round(stats.avgDailySpend * 0.8 * 100) / 100;
+    const size = userLimits.limitCanSizeMl ?? 250;
     onSaveLimits({
       ...userLimits,
+      limitCanSizeMl: size,
       dailySpendLimit: lowerDailyLimit,
+      dailyCanLimit: canLimitFromSpend(lowerDailyLimit, size),
     });
   };