Remove tray icon functionality

[Copilot]

Removes unnecessary system tray integration from the application.

Core Changes

• main/index.js: Removed Tray and nativeImage imports, createTray() function, and tray initialization. Window now quits on close instead of hiding to tray.
• Build scripts: Deleted scripts/generate-tray-icon.js and assets/tray-icon.png
• package.json: Removed generate-tray script, updated generate-all to only generate application icons

Documentation

• Removed tray references from README.md, DEVELOPMENT.md, and .github/copilot-instructions.md

The application now follows standard desktop behavior where closing the window quits the application.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Remove tray icon functionality</issue_title>
<issue_description>The tray icon is not necessary. Remove all tray icon functionality across the app.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Remove tray icon functionality #16

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