Remove init_script system timezone fallback that poisons storage (#560)

The else branch in _build_init_script() reads the system timezone via
Intl.DateTimeFormat().resolvedOptions().timeZone and stores it via
setTimezone(). When geoip resolves a different timezone (set later via
CAMOU_CONFIG/launch_options), the storage value from the init_script
takes precedence — workers read the wrong timezone and the C++ MaskConfig
fallback (PR #546) is never reached.

Fix: only call setTimezone() when an explicit timezone value is provided.
When omitted, timezone propagation is handled entirely by the C++ side
(SetNewDocument + TimezoneManager::GetTimezone MaskConfig fallback).

Companion to #546 (Fix worker timezone leak when using geoip/proxy).

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pythonlib/camoufox/fingerprints.py

@@ -373,16 +373,17 @@ def _build_init_script(values: Dict[str, Any]) -> str:
                 f'  if (typeof w.setScreenColorDepth === "function") w.setScreenColorDepth({scd});'
             )
 
-    # Timezone (always call to trigger self-destruct)
+    # Timezone — only call setTimezone() when we have an explicit value.
+    # Without this, the C++ MaskConfig fallback (from CAMOU_CONFIG set by geoip
+    # in launch_options) handles timezone for both main thread and workers via
+    # SetNewDocument() and TimezoneManager::GetTimezone().
+    # The old fallback read system TZ and poisoned RoverfoxStorageManager,
+    # preventing MaskConfig from ever being consulted.
     tz = values.get('timezone')
     if tz:
         lines.append(
             f'  if (typeof w.setTimezone === "function") w.setTimezone({_json.dumps(tz)});'
         )
-    else:
-        lines.append(
-            '  if (typeof w.setTimezone === "function") w.setTimezone(Intl.DateTimeFormat().resolvedOptions().timeZone);'
-        )
 
     # WebRTC IP
     ip = values.get('webrtcIP')