feat: implement API response caching with node-cache

- Add in-memory cache middleware with configurable TTL
- Cache GET endpoints: streets (5min), events (2min), posts (1min), rewards (10min)
- Automatic cache invalidation on POST/PUT/DELETE operations
- Add cache statistics endpoint (GET /api/cache/stats)
- Add cache management endpoint (DELETE /api/cache)
- Cache hit rate tracking and monitoring
- Pattern-based cache invalidation
- Optimized for Raspberry Pi deployment (lightweight in-memory)

🤖 Generated with Claude

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

backend/routes/streets.js

@@ -8,12 +8,14 @@ const {
   createStreetValidation,
   streetIdValidation,
 } = require("../middleware/validators/streetValidator");
+const { getCacheMiddleware, invalidateCacheByPattern } = require("../middleware/cache");
 
 const router = express.Router();
 
 // Get all streets (with pagination and filtering)
 router.get(
   "/",
+  getCacheMiddleware(300), // Cache for 5 minutes
   asyncHandler(async (req, res) => {
     const { buildPaginatedResponse } = require("../middleware/pagination");
 
@@ -81,6 +83,7 @@ router.get(
 router.get(
   "/:id",
   streetIdValidation,
+  getCacheMiddleware(300), // Cache for 5 minutes
   asyncHandler(async (req, res) => {
     const street = await Street.findById(req.params.id);
     if (!street) {
@@ -109,6 +112,9 @@ router.post(
       location,
     });
 
+    // Invalidate streets cache
+    invalidateCacheByPattern('/api/streets');
+
     res.json(street);
   }),
 );
@@ -156,6 +162,9 @@ router.put(
       user.stats.streetsAdopted = user.adoptedStreets.length;
       await user.save();
 
+      // Invalidate streets cache
+      invalidateCacheByPattern('/api/streets');
+
       // Award points for street adoption using CouchDB service
       const updatedUser = await couchdbService.updateUserPoints(
         req.user.id,