Connect the scraper to the sidecar instead of launching Chromium

fetchArtistHeaderFromSpotify currently launches a bundled Chromium with sandboxing disabled (--no-sandbox, --disable-web-security) inside the API process. Swap the launch for a connection to the sidecar.

• puppeteer.launch(...) becomes puppeteer.connect({ browserWSEndpoint }) pointing at the browserless service, endpoint + token from env
• Switch the dependency from puppeteer to puppeteer-core (no bundled Chromium download)
• Try without the stealth plugin first, browserless often passes where local headless gets flagged; bring it back only if the captcha shell shows up
• The selector logic, fallbacks and fake mode stay as they are