feat: Template library

[ikorich]

Summary

Pre-built templates for common code comparison patterns.

Motivation

Quick start with best practices for Swift, React, Python, etc.

Templates to Include

• Swift: Optional handling
• React: Hooks vs class components
• Python: List comprehension vs loops
• General: Error handling patterns

Implementation

• Bundled template JSON files
• Template browser UI
• Apply template to current comparison

Acceptance Criteria

• Template browser accessible
• At least 5 built-in templates
• One-click apply template
• Templates load correctly

Story Points

5 points