Selected PUPPETEER_EXECUTABLE_PATH before probing system browser installations so compatible headless-shell binaries remain usable by the shared daemon.
Added an isolated Windows candidate-selection regression probe.
Fixes#7601
Add the executable names and absolute paths that are unique to Ungoogled
Chromium to the Linux branch of systemChromiumCandidates(), including the
system-wide and per-user Flatpak shims for
io.github.ungoogled_software.ungoogled_chromium.
The entries are appended after the existing ones, so a stock Chrome or
Chromium install still wins and PUPPETEER_EXECUTABLE_PATH keeps working
exactly as before.
Closes#7509
metaphorics