feat: implement analytics endpoints (task 28)

- Created analytics service with summary, trends, comparison, and aggregated data methods
- Implemented 5 analytics endpoints: summary, trends, comparison, aggregated, and CSV export
- Added time series data with day/week/month interval support
- Implemented period-over-period comparison metrics with percentage changes
- Added CSV export functionality using json2csv
- Updated frontend analytics service to unwrap API responses
- Fixed chart components to work with new data structure (reportCount, eventCount, litterCollected)
- Updated TypeScript types to match backend API structure
- All endpoints tested and verified working

Requirements satisfied: 5.1, 5.2, 5.3, 5.4, 5.5

server/package-lock.json

@@ -18,6 +18,7 @@
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         "express-validator": "^7.2.0",
         "helmet": "^8.0.0",
+        "json2csv": "^6.0.0-alpha.2",
         "multer": "^1.4.5-lts.1",
         "node-cron": "^4.2.1",
         "redis": "^5.9.0",
@@ -26,6 +27,7 @@
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+        "@types/json2csv": "^5.0.7",
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@@ -778,6 +780,12 @@
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@@ -841,6 +849,16 @@
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       "license": "MIT"
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+      "license": "MIT",
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@@ -1064,6 +1082,15 @@
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@@ -1683,12 +1710,37 @@
         "node": ">=14"
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+        "lodash.get": "^4.4.2"
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+      "bin": {
+        "json2csv": "bin/json2csv.js"
+      },
+      "engines": {
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+        "npm": ">= 6.13.0"
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+      "deprecated": "This package is deprecated. Use the optional chaining (?.) operator instead.",
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