fix: wrap hover_preset_button in Obx for reactive theme updates

[vibhutomer]

Description

This PR addresses a UI state management leak in hover_preset_button.dart. Previously, the button's background color relied on a reactive GetX variable (themeController.primaryColor.value) but was not wrapped in an Obx observer. This caused the button to get "stuck" on the previous theme's color palette when a user switched between Light Mode and Dark Mode.

Proposed Changes

• Wrapped the returned ElevatedButton inside hoverPresetButton with an Obx(() => ...) stream observer.
• The button now properly listens to themeController state changes and reactively updates its UI the instant the theme is toggled.

Fixes #945

Checklist

• Tests have been added or updated to cover the changes
• Documentation has been updated to reflect the changes
• Code follows the established coding style guidelines
• All tests are passing