* Fix notification deduplication to prevent pile-up in navbar (#944)
When tasks/projects remained pending for multiple days, duplicate
notifications accumulated in the navbar instead of showing only the
most recent one.
Updated notification services to properly handle existing notifications:
- Delete unread notifications before creating new ones
- Respect dismissed notifications (don't recreate)
- Respect read notifications (don't duplicate)
Changes:
- Updated dueTaskService, deferredTaskService, and dueProjectService
- Added comprehensive unit tests with 8 test cases
Fixes#944
* Fix lint errors and add GitHub bug template reminder to docs
