Refactor: Use sender instead of BlogPostWebView in CoreWebView2Initialized

[seer-by-sentry]

Resolved / Related Issues

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• Closes FILES-APP-4F2

Steps used to test these changes

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1. The issue was that: WebView2 event handler accesses disposed BlogPostWebView.CoreWebView2 instead of valid sender.CoreWebView2, causing NullReferenceException.
2. Use the sender parameter in the CoreWebView2Initialized event handler instead of directly referencing BlogPostWebView.
3. This change improves code clarity and avoids potential issues if the WebView2 instance changes.
4. This fix was generated by Seer in Sentry, triggered by Yair. 👁️ Run ID: 1345253
5. Not quite right? Click here to continue debugging with Seer.

[Copilot]

Pull Request Overview

This PR fixes a NullReferenceException in the WebView2 event handler by using the sender parameter instead of directly accessing BlogPostWebView.CoreWebView2. This change prevents accessing a potentially disposed WebView2 instance and improves code robustness.

• Replaces direct BlogPostWebView.CoreWebView2 references with sender.CoreWebView2 in the event handler
• Uses the sender parameter consistently for WebView2 configuration and script injection
• Maintains existing functionality while fixing the disposal-related crash

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