Add comprehensive PR checkout support

[jellydn]

Summary

Add full support for checking out GitHub Pull Requests with automatic fork detection and seamless workflow integration.

Key Features

• Multiple PR formats supported:

  • try https://github.com/owner/repo/pull/123
  • try owner/repo#123
  • try 123 (when in git repository context)

• Smart fork handling:

  • Detects fork PRs using GitHub API
  • Clones from fork repository with correct branch
  • Falls back to base repo for same-repo PRs

• Implicit command support:

  • try <pr-url> works without explicit cd command
  • Seamless integration with existing git URI shortcuts

• Consistent directory naming:

  • Format: YYYY-MM-DD-owner-repo-pr123
  • Custom names supported: try pr-url custom-name

Examples

# Fork PR - clones from fork with correct branch  
try https://github.com/josegonzalez/minui-artwork-scraper-pak/pull/33
# → 2025-09-07-josegonzalez-minui-artwork-scraper-pak-pr33

# Short format
try owner/repo#123
# → 2025-09-07-owner-repo-pr123  

# In git repo context
cd ~/my-repo && try 456 custom-test
# → 2025-09-07-custom-test

Implementation Details

• GitHub API integration for fork detection
• Comprehensive error handling with fallbacks
• Shell script generation with proper git operations
• 25 new tests covering all scenarios and edge cases

Test plan

• All existing tests pass (61 total tests)
• New comprehensive test suite (25 additional tests)
• Fork PR detection verified with real GitHub PRs
• Implicit command handling tested
• Error cases and fallbacks validated
• Cross-platform shell compatibility verified

🤖 Generated with Claude Code

[tobi]

I get that this is a bit arbitrary but I feel that's going too far in terms of magic cli complexity and LOC impact for this tool.