Add Super Productivity as open-source alternative to Todoist/TickTick

## Super Productivity

**Repository:** https://github.com/johannesjo/super-productivity
**Website:** https://super-productivity.com
**License:** MIT
**GitHub Stars:** 18k+
**Platforms:** Windows, macOS, Linux, Android, iOS, Web

### Description
Super Productivity is an open-source task manager and time tracker. It combines to-do lists, timeboxing, Pomodoro timer, and time tracking with native integrations for Jira, GitHub, GitLab, Redmine, OpenProject, and other issue trackers.

### Alternative to
- Todoist
- TickTick
- Any.do
- Microsoft To Do

### Key capabilities
- Task management with subtasks and tags
- Time tracking and timeboxing
- Pomodoro timer
- Kanban board and Eisenhower matrix views
- Native Jira, GitHub, GitLab integration
- All data stored locally (privacy-first, zero telemetry)
- Available on all major platforms

Actively maintained since 2016.