Switch Playwright to headless — Xvfb fails on Proxmox LXC kernels

Xvfb exits immediately on the production LXC (no framebuffer device
support), so headed mode was never working. Switch to headless=True
and remove Xvfb from the Dockerfile entirely.

Stealth coverage is unchanged: playwright-stealth patches webdriver,
plugins and chrome.runtime; the residential proxy + sticky session
provide the GB residential fingerprint; homepage warmup carries real
session cookies into the search. --enable-unsafe-swiftshader and
--disable-blink-features=AutomationControlled are kept.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/services/scraper_backends/playwright_local.py

@@ -159,14 +159,17 @@ class PlaywrightLocalBackend(ScraperBackend):
             if self._playwright is None:
                 self._playwright = await async_playwright().start()
             launch_kwargs = dict(
-                # Headful under xvfb — far cleaner fingerprint than headless.
-                headless=False,
+                # Headless — stealth patches + residential proxy + session
+                # cookies cover the fingerprint; headed+xvfb is unreliable
+                # in Proxmox LXC kernels where Xvfb exits immediately.
+                headless=True,
                 args=[
                     '--disable-blink-features=AutomationControlled',
                     '--no-sandbox',
                     '--disable-dev-shm-usage',
                     '--disable-features=IsolateOrigins,site-per-process',
-                    '--start-maximized',
+                    '--disable-gpu',
+                    '--enable-unsafe-swiftshader',
                 ],
             )
             # Proxy is set at launch (Chromium binds the sticky session, which