When the WebUI server is launched from a venv python whose PATH does not
include git (e.g. hermes-agent venv on Windows), shutil.which('git')
returns None and WEBUI_VERSION falls back to 'unknown'. That freezes the
?v=<stamp> static-asset cache key, so browsers keep serving stale cached
ui.js/messages.js even after the server is restarted with fixed code —
frontend fixes silently never reach clients (recurring scroll jump-back).
Add a Windows fallback to _resolve_git_executable(): read the
Git-for-Windows registry InstallPath (HKLM + WOW6432Node + HKCU), then
probe common install dirs. Mirrors the existing darwin /usr/bin/git
fallback. No behavior change on posix or when git is already on PATH.