#19223: fix: add WSL2 Windows browser detection for Linux platform

Fixes #19185 ## What changed - Added WSL2 detection to check for "Microsoft" or "WSL2" in /proc/version - When running on WSL2, checks for Windows browsers mounted at /mnt/c/ (Brave, Chrome, Edge, Chromium) - Both detectDefaultChromiumExecutableLinux() and findChromeExecutableLinux() now check for WSL2 Windows browsers first ## AI-assisted contribution - This fix was generated by an AI agent (OpenClaw cron: gh-issues-fix) - Testing depth: validated with pnpm build && pnpm lint - The fix addresses the root cause by detecting Windows browsers when running under WSL2 <!-- greptile_comment --> <h3>Greptile Summary</h3> This PR adds WSL2 detection to the Linux browser executable resolution, allowing the app to find Windows browsers mounted at `/mnt/c/` when running under WSL2. Two new helper functions (`isWsl2()` and `detectWsl2WindowsBrowser()`) are introduced and called from both `detectDefaultChromiumExecutableLinux()` and `findChromeExecutableLinux()`. - **Logic concern**: In `detectDefaultChromiumExecutableLinux`, the WSL2 check runs before `xdg-settings`/`xdg-mime`, meaning it will override the user's explicitly configured default browser on WSL2 systems. The WSL2 check would be better placed as a fallback after the standard detection fails. - **Style**: `isWsl2()` spawns `cat` to read `/proc/version` when `fs.readFileSync` (already imported) would be simpler and more efficient. - **Missing tests**: No tests were added for the new WSL2 detection logic, despite the existing test file (`chrome.default-browser.test.ts`) already having the mocking infrastructure in place. <h3>Confidence Score: 3/5</h3> - Functionally works for the target WSL2 use case but has a behavioral issue where it overrides user's default browser preference on WSL2 - The core WSL2 detection and path resolution logic is correct and handles edge cases (non-Linux platforms, missing /proc/version). However, the placement of the WSL2 check in detectDefaultChromiumExecutableLinux bypasses the user's configured default browser, which is a meaningful behavioral issue. No tests were added for the new code paths. - Pay close attention to `src/browser/chrome.executables.ts` — the WSL2 detection placement in `detectDefaultChromiumExecutableLinux` overrides user's default browser preference _{Last reviewed commit: 9ca2990} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->