Add Facebook username validation support (social category)

user_scanner/social/facebook.py

@@ -0,0 +1,27 @@
+from ..core.orchestrator import status_validate
+
+
+def validate_facebook(user: str) -> int:
+    """
+    Checks if a Facebook username is available.
+
+    Strategy:
+    - Facebook profile URLs follow the pattern: https://www.facebook.com/<username>
+    - Existing usernames typically return HTTP 200.
+    - Non-existing usernames are expected to return HTTP 404 or a similar not-found status.
+    - We rely on HTTP status codes using status_validate.
+    """
+    url = f"https://www.facebook.com/{user}"
+
+    headers = {
+        "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/141.0.0.0 Safari/537.36",
+        "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
+        "Accept-Encoding": "gzip, deflate, br",
+        "Accept-Language": "en-US,en;q=0.9",
+        "Upgrade-Insecure-Requests": "1",
+    }
+
+    # 404 -> available, 200 -> taken
+    return status_validate(url, 404, 200, headers=headers, follow_redirects=True)
+
+