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

🤖 Generated with [AI Assistant]

Co-Authored-By: AI Assistant <noreply@ai-assistant.com>

backend/scripts/migrate-to-couchdb.js

@@ -292,7 +292,7 @@ class MigrationService {
       
       // Batch insert
       if (transformedDocs.length > 0) {
-        const result = await couchdbService.bulkDocs({ docs: transformedDocs });
+        const result = await couchdbService.bulkDocs(transformedDocs);
         
         // Count successful migrations
         const successful = result.filter(r => r.ok).length;
@@ -490,7 +490,7 @@ class MigrationService {
       ];
       
       if (allDocs.length > 0) {
-        const result = await couchdbService.bulkDocs({ docs: allDocs });
+        const result = await couchdbService.bulkDocs(allDocs);
         const successful = result.filter(r => r.ok).length;
         console.log(`✅ Successfully updated ${successful}/${allDocs.length} documents with relationship data`);
       }