fix: block F5/Refresh in chat webview to prevent blank screen

[laileni-aws]

Problem

When the Amazon Q Chat view has focus and the user presses F5 (or triggers a browser refresh via Cmd+R / context menu), the entire chat UI disappears and is replaced by a blank white screen. The chat does not recover without manually closing and reopening the view.

Prevents the chat webview from going blank when the user accidentally triggers a browser refresh (F5, Cmd+R, or context menu reload).

The chat webview uses browser.setText(html) to render content inline with no backing URL. A refresh causes the browser to navigate to about:blank, wiping the UI entirely.

Fix:

• Added a LocationListener that blocks any navigation to about:blank, preventing the blank screen regardless of how the refresh is triggered.
• Added a KeyListener that intercepts F5 keypress and suppresses it as an additional safeguard.

Testing:

1. Open the Amazon Q Chat view and confirm it loads normally
2. Press F5 with the chat view focused → chat UI remains intact
3. Try Cmd+R (macOS) or right-click → Reload if available → chat UI remains intact
4. Confirm normal chat functionality (send/receive messages) is unaffected

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