Add descriptions to all .cursor/rules files

- Add brief descriptions to YAML frontmatter for all rule files
- Descriptions explain the purpose and content of each rule
- Follow consistent format matching ml-systems-course-context.mdc
- Improve rule discoverability and understanding

Files updated:
- user-preferences.mdc: User preferences and development conventions
- tinytorch-project-structure.mdc: Dual-structure architecture guide
- testing-patterns.mdc: Testing standards with pytest and real data
- nbdev-educational-pattern.mdc: Educational NBDev patterns
- module-development-best-practices.mdc: Real Data, Real Systems principles
- git-workflow.mdc: Git workflow guidelines for incremental commits
- development-workflow.mdc: Complete development workflow with tito CLI
- cli-patterns.mdc: CLI development patterns for tito tool

.cursor/rules/cli-patterns.mdc

@@ -1,6 +1,9 @@
 ---
+description: CLI Development Patterns for TinyTorch
+globs:
 alwaysApply: false
 ---
+
 # CLI Development Patterns for TinyTorch
 
 ## Command Architecture
@@ -165,7 +168,7 @@ in_venv = (
 6. **Handle edge cases** - Missing files, invalid arguments, etc.
 7. **Provide progress feedback** - For long-running operations
 8. **Use consistent styling** - Colors, borders, and formatting
-description:
+
 globs:
 alwaysApply: false
 ---