feat: Complete critical CouchDB migration fixes and infrastructure improvements

- Fix design document initialization with proper null handling
- Fix bulk operations in migration script (bulkDocs method signature)
- Remove hardcoded credentials from docker-compose.yml
- Fix test infrastructure incompatibility (use npm/Jest instead of bun)
- Implement comprehensive database indexes for performance
- Add health check endpoint for Docker container monitoring
- Create 7 design documents: users, streets, tasks, posts, badges, transactions, general
- Update jest.setup.js with proper mock exports
- Add .env.example with secure defaults

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backend/package.json

@@ -3,10 +3,10 @@
   "version": "1.0.0",
   "main": "index.js",
   "scripts": {
-    "test": "cross-env NODE_ENV=test jest",
-    "test:watch": "cross-env NODE_ENV=test jest --watch",
-    "test:coverage": "cross-env NODE_ENV=test jest --coverage",
-    "test:verbose": "cross-env NODE_ENV=test jest --verbose",
+    "test": "cross-env NODE_ENV=test node_modules/.bin/jest",
+    "test:watch": "cross-env NODE_ENV=test node_modules/.bin/jest --watch",
+    "test:coverage": "cross-env NODE_ENV=test node_modules/.bin/jest --coverage",
+    "test:verbose": "cross-env NODE_ENV=test node_modules/.bin/jest --verbose",
     "start": "bun server.js",
     "dev": "bunx nodemon server.js",
     "seed:badges": "bun scripts/seedBadges.js",