feat(electron): enable webviewTag on mainWindow for advanced extension support

[arindam-sahoo]

Description
This PR updates the webPreferences configuration of the mainWindow in Electron to explicitly enable webviewTag: true.

Enabling the <webview> tag allows extensions (like the new Phone Browser) to render external content in a sandboxed, isolated environment that acts as a fully featured native browser.

Changes Made

• electron/main.cts: Added webviewTag: true to the mainWindow initialization options.

Testing Done

• Verified that KoBar still boots up correctly.
• Verified that extensions utilizing <webview> (like the Phone Browser) can successfully load external websites and perform full navigation without triggering CSP or iframe rejections.

Fixes #66

Type of Change

Please check the options that are relevant:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• UI/UX improvement (visual changes or enhancements)
• Documentation update

Checklist

Please check all the boxes before submitting your PR:

• I have tested my code locally and it works flawlessly.
• I am strictly sure that my changes DO NOT break KoBar's "Ghost Window" (transparent window) and click-through logic.
• I have added necessary descriptions and comments to my code.
• My code does not generate any new warnings or errors in the console.