docs: integrate Template System Design across redesign documentation

- Enhanced phase2-analysis/02-automation-and-tooling.md with template engine analysis
  * Comprehensive comparison of Tera vs Askama template engines
  * Template type system architecture with Rust code examples
  * Implementation benefits and integration considerations

- Enhanced phase2-analysis/04-testing-strategy.md with template testing strategy
  * Multi-level template validation approach (syntax, configuration, integration)
  * Template testing implementation examples and frameworks
  * Comprehensive testing strategy for template-based configurations

- Added phase3-design/template-system-adr.md as new architectural decision record
  * Template Type Wrapper Architecture design and rationale
  * Tera template engine selection with detailed comparison
  * Phased implementation strategy and risk mitigation
  * Complete code examples and usage patterns

This integration extracts and strategically distributes template system insights
from the PoC analysis across appropriate documentation phases, establishing the
architectural foundation for production-grade configuration management.

Author: josecelano

docs/redesign/phase2-analysis/02-automation-and-tooling.md

@@ -59,6 +59,83 @@ ensuring consistency and reproducibility.
    - Go's `text/template` package (if using Go).
    - Tools like Ansible for more complex configuration and orchestration tasks.
 
+## Template Engine Analysis
+
+### Current Template Limitations
+
+The existing PoC uses `envsubst` for basic variable substitution, which has significant
+limitations for complex configuration scenarios:
+
+- **No Type Safety**: Variables are processed as raw strings without validation
+- **Limited Logic**: Cannot handle conditional sections or iterative constructs
+- **Error Prone**: Silent failures on missing variables or syntax errors
+- **No Validation**: Template syntax errors only discovered at runtime
+
+### Template Engine Evaluation
+
+For a Rust-based redesign, several template engines were evaluated:
+
+#### Tera Template Engine (Recommended)
+
+**Strengths**:
+
+- **Django/Jinja2-like Syntax**: Familiar to developers with web framework experience
+- **Rich Feature Set**: Supports filters, macros, inheritance, and conditional logic
+- **Excellent Error Handling**: Comprehensive error messages with line numbers
+- **Active Development**: Well-maintained with regular updates
+- **Template Inheritance**: Supports base templates and block overrides
+
+**Implementation Benefits**:
+
+- **Complex Configuration Logic**: Handle environment-specific conditionals
+- **Data Structure Support**: Process nested configurations and arrays
+- **Validation Integration**: Validate templates during build phase
+- **Developer Experience**: Clear error messages and debugging support
+
+#### Askama (Alternative Consideration)
+
+**Strengths**:
+
+- **Compile-time Safety**: Templates validated during compilation
+- **Zero Runtime Dependencies**: Templates compiled to Rust code
+- **Performance**: Faster execution due to compile-time generation
+
+**Limitations**:
+
+- **Less Flexible**: Limited runtime template modification
+- **Learning Curve**: Custom syntax different from established standards
+- **Ecosystem**: Smaller community compared to Tera
+
+### Template Type System Architecture
+
+The template system should implement a type-safe wrapper approach:
+
+```rust
+// Template type wrapper for type safety
+pub struct TemplateConfig<T> {
+    pub template_path: PathBuf,
+    pub output_path: PathBuf,
+    pub context: T,
+    pub validation_rules: Vec<ValidationRule>,
+}
+
+// Environment-specific configuration types
+#[derive(Serialize, Deserialize)]
+pub struct NginxConfig {
+    pub tracker_domain: String,
+    pub grafana_domain: String,
+    pub ssl_enabled: bool,
+    pub ports: PortConfiguration,
+}
+```
+
+This approach provides:
+
+- **Compile-time Validation**: Type checking prevents configuration errors
+- **IDE Support**: Auto-completion and validation in development environments
+- **Documentation**: Self-documenting configuration structure
+- **Testing**: Unit tests can validate template rendering logic
+
 ## Provisioning Strategy Analysis
 
 ### Current Approach: Cloud-init + Shell Scripts

docs/redesign/phase2-analysis/04-testing-strategy.md

@@ -159,9 +159,88 @@ for most test scenarios:
 - Validate API endpoints, UDP/HTTP tracker protocols
 - Use testcontainers for database and external service mocking
 
+**Template System Testing**:
+
+- **Unit Testing**: Validate individual template rendering with known inputs
+- **Integration Testing**: Test complete configuration generation workflows
+- **Validation Testing**: Verify generated configurations pass syntax checks
+- **Type Safety Testing**: Ensure template context types match expected schemas
+
 **Infrastructure Validation**:
 
 - Reserve VM/cloud testing for infrastructure-specific scenarios
 - Use staging environments for periodic full integration validation
 - Implement blue-green deployment testing in production-like environments
 - Focus VM testing on provider-specific networking, security, and performance
+
+### Template System Testing Strategy
+
+#### Multi-Level Template Validation
+
+The template system requires comprehensive testing at multiple levels to ensure
+configuration correctness and prevent deployment failures:
+
+##### Level 1: Template Syntax Validation
+
+- **Tera Template Parsing**: Validate template syntax during compilation
+- **Context Schema Validation**: Ensure template context matches expected types
+- **Missing Variable Detection**: Catch undefined variables before rendering
+- **Template Inheritance Testing**: Validate base template and block override logic
+
+##### Level 2: Configuration Generation Testing
+
+- **Input Validation**: Test with various environment configurations
+- **Output Verification**: Validate generated configuration file syntax
+- **Cross-Environment Testing**: Ensure templates work across development/staging/production
+- **Edge Case Handling**: Test with minimal, maximal, and invalid input scenarios
+
+##### Level 3: Integration Testing with Target Services
+
+- **Nginx Configuration Testing**: Validate generated nginx.conf syntax and logic
+- **Docker Compose Validation**: Ensure generated compose files are valid YAML
+- **Service Integration**: Test that generated configurations work with actual services
+- **Health Check Integration**: Verify configurations enable proper service health monitoring
+
+#### Template Testing Implementation
+
+```rust
+#[cfg(test)]
+mod template_tests {
+    use super::*;
+
+    #[test]
+    fn test_nginx_template_rendering() {
+        let config = NginxConfig {
+            tracker_domain: "tracker.test.local".to_string(),
+            grafana_domain: "grafana.test.local".to_string(),
+            ssl_enabled: false,
+            ports: PortConfiguration::default(),
+        };
+
+        let template = TemplateConfig::new("nginx.conf.tera", config);
+        let result = template.render().unwrap();
+
+        // Validate nginx syntax
+        assert!(validate_nginx_syntax(&result).is_ok());
+        assert!(result.contains("server_name tracker.test.local"));
+    }
+
+    #[test]
+    fn test_template_context_validation() {
+        let invalid_config = NginxConfig {
+            tracker_domain: "".to_string(), // Invalid empty domain
+            // ... other fields
+        };
+
+        let template = TemplateConfig::new("nginx.conf.tera", invalid_config);
+        assert!(template.validate().is_err());
+    }
+}
+```
+
+This testing approach provides:
+
+- **Early Error Detection**: Catch template issues during development
+- **Regression Prevention**: Ensure template changes don't break existing functionality
+- **Configuration Validation**: Verify generated configurations are syntactically correct
+- **Type Safety Assurance**: Prevent runtime errors through compile-time validation