Right/left icons are inconsistent across the datepicker and migration buttons

Where did this happen?

Local code with an up-to-date main branch, Hosted (app.compasscalendar.com)

Expected Behavior

The right/left icons are consistent across the entire app. Specifically, the month picker should use the arrow icons that we use in the day planner for the migration functionality.

Current Behavior

The month picker uses different icons compared to the events

Icons to replace - Sidebar <img width="314" height="334" alt="Image" src="https://github.com/user-attachments/assets/09560041-ebec-4035-af4f-7ccfddeab0e8" />

Icons to replace - Allday form <img width="496" height="387" alt="Image" src="https://github.com/user-attachments/assets/d622f47b-05e4-4604-b022-743330728d11" />

Desired arrow icon <img width="543" height="456" alt="Image" src="https://github.com/user-attachments/assets/2313f2e4-68c6-4c6e-ba9c-cb27d6bf11f3" />

Steps to Reproduce

1. Type SHIFT+2 or click the month icon in the sidebar to show the month widget
2. Notice the arrow styles
3. Click the open space on the all-day row
4. All-day form will open
5. Click the date input
6. Month widget will open
7. Notice the arrow styles
8. Go to /day
9. Create a task
10. Hover over task
11. Notice the arrow styles

Possible Solution

Update the month widget to use the icon

Context

The month widget might currently be using simple text for "<" and ">", which is dependent on the font. We should decouple the widget from the font selection, so that changing the font size/style doesn't affect the widget

<!-- upstream-issue: SwitchbackTech/compass#1328 -->