ci(github): add linting and improve CI workflow

- Add ESLint configuration for backend TypeScript code
- Include linting step in backend quality checks
- Add linting step to GitHub Actions CI workflow
- Enable configurable Prisma query logging via PRISMA_LOG_QUERIES environment variable
- Update PrismaService to support dynamic log levels based on PRISMA_LOG_QUERIES
- Replace BadRequestException with UnauthorizedException in receipt import security tests

flutter/analysis_options.yaml

@@ -0,0 +1,5 @@
+include: package:flutter_lints/flutter.yaml
+
+linter:
+  rules:
+    avoid_print: true