Add Recharts charts to Monthly Summary and Annual Overview

Monthly Summary:
- Spending breakdown donut (bills / variable / one-time)
- Variable spending by category bar chart
- Added actuals.by_category to /api/summary/monthly response

Annual Overview:
- Income vs. spending grouped bar chart
- Surplus/deficit bar chart (green/red per month)
- Stacked variable spending by category across all months
- New /api/summary/annual endpoint (single DB round trip for full year)
- AnnualOverview now uses /api/summary/annual instead of 12 parallel calls

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/package.json

@@ -9,7 +9,8 @@
   "dependencies": {
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
-    "react-router-dom": "^6.23.1"
+    "react-router-dom": "^6.23.1",
+    "recharts": "^3.8.0"
   },
   "devDependencies": {
     "@vitejs/plugin-react": "^4.3.0",