Add GH_PATH support for GitHub-specific repository organization

[miguelalcalde]

Summary

• Add GH_PATH environment variable support for organizing GitHub repositories in $GH_PATH/<owner>/<repo> structure (e.g., ~/github/tobi/try)
• Implement source switching in TUI with Ctrl-G to toggle between tries and GitHub sources

$ ~/github tree
.
├── miguelalcalde
│   ├── ecomm-dummy
│   ├── personal-crm-app
│   ├── tech-shop
├── mikemajara
│   ├── go-link-tree
│   ├── notion-cms
│   ├── test-repo-1
│   ├── test-repo-2
│   └── test-repo-3
└── tobi
    └── try

Changes

New Feature: GH_PATH Support

When GH_PATH is set:

• GitHub repositories are cloned to $GH_PATH/<owner>/<repo> instead of date-prefixed directories
• If the directory already exists, just cds into it without re-cloning
• TUI displays GitHub repositories with owner/repo format (e.g., toby/try)

TUI Enhancements

• Ctrl-G: Toggle between sources (All → Tries only → GitHub only)
• Header shows current source indicator: (Tries + GitHub), (Tries only), or (GitHub only)
• "Create new" option is disabled when viewing GitHub-only source

Delete Safety Validation

• Items from tries source validate against TRY_PATH
• Items from GitHub source validate against GH_PATH
• Delete script now uses absolute paths to support mixed deletions

Test Plan

• [ ] Set GH_PATH=~/github and clone a GitHub repo: try clone https://github.com/user/repo
• [ ] Verify repo is created at ~/github/user/repo
• [ ] Launch TUI and press Ctrl-G to cycle through source filters
• [ ] Verify GitHub repos display as owner/repo format
• [ ] Test deleting a GitHub repo with Ctrl-D → type YES
• [ ] Test deleting items from both sources in a single operation
• [ ] Verify clone skips if directory already exists when using GH_PATH