feat: add WSL2 Windows Firefox cookie extraction for X auth

On WSL2, native Linux Firefox typically has no x.com cookies since users
browse in Windows. Chromium browsers (Edge, Chrome, Brave) encrypt cookies
with DPAPI/app-bound encryption, making them inaccessible without admin
privileges. Windows Firefox stores cookies unencrypted in SQLite, readable
directly through the /mnt/c mount.

The cookie extractor now detects WSL2 via /proc/version, locates Windows
Firefox profiles under /mnt/c/Users/*/AppData/Roaming/Mozilla/Firefox,
and falls back to them when Linux Firefox yields no results. Reports
source as "firefox-wsl" to distinguish from native.

Also fixes profile resolution priority: Install* sections (Firefox >= 67)
now take precedence over the legacy Default=1 flag, which could select a
stale profile on multi-profile installations.

tests/test_cookie_extract.py

@@ -153,6 +153,9 @@ class TestExtractFirefoxCookies:
         with patch(
             "scripts.lib.cookie_extract._get_firefox_profiles_dir",
             return_value=None,
+        ), patch(
+            "scripts.lib.cookie_extract._is_wsl",
+            return_value=False,
         ):
             result = extract_firefox_cookies(".x.com", ["auth_token"])
 
@@ -167,6 +170,9 @@ class TestExtractFirefoxCookies:
         with patch(
             "scripts.lib.cookie_extract._get_firefox_profiles_dir",
             return_value=profiles_dir,
+        ), patch(
+            "scripts.lib.cookie_extract._is_wsl",
+            return_value=False,
         ):
             result = extract_firefox_cookies(".x.com", ["auth_token", "ct0"])
 
@@ -185,6 +191,9 @@ class TestExtractFirefoxCookies:
         with patch(
             "scripts.lib.cookie_extract._get_firefox_profiles_dir",
             return_value=profiles_dir,
+        ), patch(
+            "scripts.lib.cookie_extract._is_wsl",
+            return_value=False,
         ):
             result = extract_firefox_cookies(".x.com", ["auth_token", "ct0"])