Issue 3: Complete Todo Management Feature

## Overview
Implement full CRUD operations for todo management with Supabase integration.

## Tasks
- [ ] Implement todo creation functionality
- [ ] Add todo editing capabilities
- [ ] Implement todo deletion
- [ ] Add todo completion toggle
- [ ] Implement priority filtering
- [ ] Add due date functionality
- [ ] Implement real-time updates
- [ ] Add todo search functionality
- [ ] Implement todo categories/tags
- [ ] Add bulk operations (delete, complete)

## Acceptance Criteria
- [ ] Users can create, read, update, delete todos
- [ ] Todos sync in real-time across devices
- [ ] Priority levels work correctly
- [ ] Due dates are properly handled
- [ ] Search and filtering work
- [ ] UI is responsive and user-friendly

## Technical Details
- Use Supabase real-time subscriptions
- Implement optimistic updates
- Add proper error handling
- Use existing TodoPage component structure
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