Add lead tracking parameter to demo form submission

- Replace thank you modal with redirect to /pricing?lead=1 after successful form submission
- Enables Google Analytics to track successful lead submissions via URL parameter
- Maintains all existing form validation and PostHog event tracking

Co-Authored-By: tom@reflex.dev <tom@reflex.dev>

Author: devin-ai-integration[bot]

pcweb/pages/pricing/header.py

@@ -184,8 +184,7 @@ def submit(self, form_data: dict[str, Any]):
             # Send to PostHog for all submissions
             yield QuoteFormState.send_demo_event(form_data)
 
-            # Show thank you modal for all submissions
-            yield ThankYouDialogState.push(True)
+            yield rx.redirect("/pricing?lead=1")
             return