Adds a simple config file (~/.config/ssr/extra-installers.txt) where
users can list installer URLs for apps not available on Homebrew or MAS
(e.g. EasyMCP Desktop, internal tools).
lib/installers.sh:
- Supports .dmg (mount → cp .app or run .pkg), .pkg, .zip
- Skips entries already present in /Applications
- Non-fatal: logs warnings and continues on failure
ssr sync: copies extra-installers.txt to <backup_dir> alongside Brewfile
ssr restore: new `extra_installers` resumable step runs after shell_deps
Format: optional-name <url> (# comments and blank lines ignored)
Example entry:
EasyMCP https://github.com/Adobe-AIFoundations/easymcp/.../EasyMCP-Desktop-3.0.3-arm64.dmg
Co-authored-by: Cursor <cursoragent@cursor.com>
