refactor: reorganize tests into three-layer architecture

- Move Docker Compose tests to application/tests/ layer
- Move Makefile and project-wide tests to tests/ layer
- Keep infrastructure tests in infrastructure/tests/ layer
- Create comprehensive test organization documentation
- Add layer-specific test scripts and README files
- Establish clear separation of concerns for test responsibilities

This fixes the mixed-layer test organization where infrastructure/tests/
contained tests belonging to different architectural layers, violating
the separation of concerns principle.

New test structure:
- infrastructure/tests/ - Infrastructure provisioning validation
- application/tests/ - Application deployment validation
- tests/ - Project-wide and cross-cutting validation

Includes governance documentation to prevent future misorganization.

Author: josecelano

application/tests/README.md

@@ -0,0 +1,121 @@
+# Application Tests
+
+This directory contains tests specific to application deployment and configuration validation.
+
+## Purpose
+
+Tests in this directory focus on:
+
+- **Application configuration validation** (Docker Compose, environment files)
+- **Application directory structure verification**
+- **Deployment script validation**
+- **Service configuration testing** (Grafana, monitoring configs)
+
+## Test Scope
+
+These tests validate application components **without performing actual deployment**.
+They are static validation tests that ensure:
+
+- Configuration files are syntactically correct
+- Required files and directories exist
+- Scripts have proper permissions
+- Service configurations are valid
+
+## Test Organization
+
+### Current Tests
+
+- `test-unit-application.sh` - Main application validation test suite
+
+### Test Categories
+
+1. **Docker Compose Validation** - Ensures `compose.yaml` is valid
+2. **Configuration Validation** - Checks `.env` templates and config files
+3. **Structure Validation** - Verifies application directory structure
+4. **Script Validation** - Checks deployment scripts exist and are executable
+5. **Service Configuration** - Validates Grafana dashboards and other service configs
+
+## Usage
+
+```bash
+# Run all application tests
+./test-unit-application.sh
+
+# Run specific test categories
+./test-unit-application.sh docker          # Docker Compose only
+./test-unit-application.sh config          # Configuration only
+./test-unit-application.sh structure       # Structure only
+./test-unit-application.sh scripts         # Scripts only
+./test-unit-application.sh grafana         # Grafana config only
+```
+
+## Test Organization Guidelines
+
+### What Belongs Here
+
+✅ **Application layer tests**:
+
+- Docker Compose file validation
+- Application configuration files (`.env`, service configs)
+- Application deployment scripts
+- Service-specific configurations (Grafana, Prometheus configs)
+- Application directory structure
+
+### What Does NOT Belong Here
+
+❌ **Infrastructure tests** (belong in `infrastructure/tests/`):
+
+- Terraform/OpenTofu configurations
+- Cloud-init templates
+- Infrastructure provisioning scripts
+- VM-level configurations
+
+❌ **Project-wide tests** (belong in `tests/` at project root):
+
+- Root-level Makefile
+- Project structure spanning multiple layers
+- Tool availability checks
+- Cross-cutting documentation
+
+## Integration with Other Test Layers
+
+This test suite is part of a three-layer testing architecture:
+
+1. **Infrastructure Tests** (`infrastructure/tests/`) - Infrastructure provisioning
+2. **Application Tests** (`application/tests/`) - Application deployment (this directory)
+3. **Project Tests** (`tests/`) - Cross-cutting project validation
+
+Each layer focuses on its specific concerns and can be run independently.
+
+## Adding New Tests
+
+When adding new application tests:
+
+1. **Categorize correctly** - Ensure the test belongs to the application layer
+2. **Follow naming conventions** - Use `test_function_name()` format
+3. **Add to main suite** - Include in `run_application_tests()` function
+4. **Update help** - Add command options if needed
+5. **Document purpose** - Explain what the test validates
+
+### Example Test Function
+
+```bash
+test_new_application_feature() {
+    log_info "Testing new application feature..."
+
+    local failed=0
+    # Test implementation here
+
+    if [[ ${failed} -eq 0 ]]; then
+        log_success "New application feature validation passed"
+    fi
+
+    return ${failed}
+}
+```
+
+## Related Documentation
+
+- [Infrastructure Tests](../infrastructure/tests/README.md)
+- [Project Tests](../tests/README.md)
+- [Testing Strategy](../docs/testing/test-strategy.md)