Refactor AppStore to Zustand

[vicksey]

Summary

Refactored the AppStore into three stores Zustand stores:
scheduleStore - Manages scheduling-related state.
snackbarStore - Handles snack bar notifications and alerts.
undoRedoStore - Tracks and manages undo/redo actions for state changes.

This will improve maintainability, reusability, and debugging in the future by breaking down our previous AppStore

Test Plan

• Verify that ALL scheduling-related functions work as expected. Calendar/Schedule behaviours:
• Ensure all snack bar functionality appear and behave correctly.
• Confirm that undo/redo functionality works across relevant components.
• Check that all functionality on AppStore hasn't been broken by the migration
• Run full regression test on all related functionality

Issues

• Finished updating all components that originally referenced AppStore to the new Zustand stores.
• Still in the process of testing all functions and fixing some bugs.

Closes #1076

To Do:

• Implement scheduleStore, snackbarStore, undoRedoStore
• Migrate logic from AppStore to new Zustand stores
• Update all references to of AppStore throughout the codebase
• Verify schedule, snack bar, and undo/redo behaviours still works after migration
• Go through merge conflicts
• Remove unnecessary code from AppStore (or the entirety of it)
• Clean up code
• Run regression tests
• Waiting until I can merge with oauth

My tests:

• Calendar/Schedule behaviours:
• Add a schedule
• Delete a schedule
• Rename a schedule
• Copy a schedule
• Switch between schedules
• Add a course to calendar
• Delete a course to calendar
• Add custom event to calendar
• Calendar events are being correctly updated on the Added pane
• Finals schedule is synced with Calendar schedule
• Calendar events can be recoloured through Calendar and Added pane
• Clear schedule
• Locations link to map pane
• Map is functional
• Download calendar functions appropriately
• Load schedule functions appropriately
• Save schedule functions appropriately
• Import a schedule from study list
• Import a schedule from ZotCourse
• Tour functions properly
• Snack bar behaviours:
• Load a schedule
• Save a schedule
• Errors?
• Undo/Redo behaviours:
• Undo last action button works
• Cntrl+Z works