* Improve upgrade command installation method detection robustness
The upgrade command was failing to detect installation method for users who installed via pnpm, yarn, or bun, showing "Could not detect installation method" errors.
## Changes Made
- **Added support for additional package managers**: Extended detection to include pnpm, yarn, and bun alongside existing npm, Homebrew, and Cargo support
- **Implemented install-time marker system**: Modified `postinstall.js` to write a `.install-method` marker file during installation, providing reliable detection that doesn't depend on fragile path heuristics
- **Enhanced path-based fallback detection**: Improved executable path analysis to better identify installation locations for all supported package managers
- **Added command probing**: Implemented fallback checks that query package managers directly to verify global installations
The detection now follows this robust hierarchy:
1. Read install-time marker file (most reliable)
2. Analyze executable path patterns
3. Probe package managers via subprocess calls
This ensures users can successfully upgrade regardless of their chosen package manager.
Fixes#954
* Add .install-method to .gitignore and note Yarn v2+ limitation
- Prevent bin/.install-method marker file from being accidentally
committed during development
- Add comment clarifying that yarn global upgrade path only works
with Yarn Classic (v1), not Yarn Berry (v2+)
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Co-authored-by: ctate <366502+ctate@users.noreply.github.com>
