feat(bootstrap)!: assume Puppeteer's browser is installed. No longer set PUPPETEER_EXECUTABLE_PATH

[iamgio]

This PR now assumes Puppeteer bundles its own browser installation for better compatibility, without relying on the user's installed browsers by default, unless the env var PUPPETEER_CHROME_SKIP_DOWNLOAD is set to true before the setup. In that case, the responsibility to set PUPPETEER_EXECUTABLE_PATH is a responsibility of the user and not Quarkdown's anymore.

This aligns with the change being made in install scripts and package manager installations: ensuring Puppeteer is using its own browser instance ensures a consistent and performant result is always provided. This fixes heavy delays and often timeouts in PDF generation whenever the installed browser version didn't match Puppeteer's.

Former PUPPETEER_EXECUTABLE_PATH assignments in bootstrap scripts have now been replaced by browser detection checks that will come in handy for future features.

[iamgio]

@alerque pinging you in case you need to update your Arch package. The updated Homebrew formula might be useful -- in particular removing PUPPETEER_CHROME_SKIP_DOWNLOAD and setting PUPPETEER_CACHE_DIR did the trick. The latter was particularly important (and hard to figure out) since Puppeteer was not launching the installer at all while in /opt, for some unknown reason.