docs: add cross-references between template documentation files

- Add 'See Also' link in templates.md pointing to architecture doc
- Add 'See Also' link in template-system-architecture.md pointing to contributing guide
- Improves discoverability between practical guide and technical documentation

Author: josecelano

docs/contributing/templates.md

@@ -2,6 +2,8 @@
 
 This document explains the correct syntax for defining variables in Tera templates used in the Torrust Tracker Deployer project.
 
+> **See Also**: For architectural details about how the template system works, see [Template System Architecture](../technical/template-system-architecture.md).
+
 ## 📝 Correct Variable Syntax
 
 All Tera template variables must use **double curly braces** with **no spaces** inside the braces:

docs/technical/template-system-architecture.md

@@ -2,6 +2,8 @@
 
 Technical documentation for contributors working with the template rendering system.
 
+> **See Also**: For practical guidance on working with templates, see [Tera Template Variable Syntax](../contributing/templates.md).
+
 ## 🏗️ System Overview
 
 The template system uses a **double indirection** approach to provide flexible infrastructure deployment while maintaining portability and customizability.