Refactor Docker and Makefile configurations for improved build processes

- Updated docker-compose.tools.yml to mount source code at /src and set working directory for backend tools, ensuring proper Go module caching.
- Modified Dockerfile.tools to install the latest golangci-lint version compatible with Go 1.24 and adjusted working directory for build-time operations.
- Enhanced Makefile to build backend tools before running tests and linting, ensuring dependencies are up-to-date and improving overall workflow efficiency.
- Refactored test and handler files to include error handling for database operations, enhancing reliability and debugging capabilities.

docker-compose.tools.yml

@@ -1,13 +1,18 @@
 # One-off tools: test, lint, fmt. Use with: docker compose -f docker-compose.tools.yml run --rm <service> <cmd>
 # Source is mounted so commands run against current code.
+# Backend: mount at /src so the image's /go module cache (from build) is not overwritten.
 
 services:
   backend-tools:
     build:
       context: .
       dockerfile: Dockerfile.tools
+    working_dir: /src
+    environment:
+      GOPATH: /go
+      GOMODCACHE: /go/pkg/mod
     volumes:
-      - .:/hnh-map
+      - .:/src
     # Default command; override when running (e.g. go test ./..., golangci-lint run).
     command: ["go", "test", "./..."]