fix(market-installer): ensure bundled Node and pnpm runtimes are used for plugin installation - #61

Summary

• Bundled pnpm dependency: Added pnpm: 10.34.5 directly to root package.json dependencies to ensure it is always included in the packaged Electron distribution.
• Node & pnpm Shims: Enhanced ensurePnpmShim in packages/dsh-desktop-market-installer to generate shims for both pnpm and node (supporting .cmd on Windows and executable shell scripts on POSIX), pointing directly to the app's bundled Node runtime (process.execPath).
• Path Resolution: Prepended both the .desktop-bin directory and the bundled Node runtime directory to PATH (handling Windows Path/PATH case differences), guaranteeing that any plugin install or subprocess runs with the bundled runtimes without requiring a system Node.js install.
• Tests: Added test assertions to test/market-installer.test.js to verify that both node and pnpm shims are properly generated.