Feature Request: Implement task dependencies for sequential workflow management

[RUS29TAM]

Problem Description

Currently, tasks in Joplin are independent with no way to define relationships. In real projects, many tasks cannot start until previous tasks are completed (prerequisites). This limits realistic project workflow planning.

Proposed Solution

Implement task dependency/link system similar to professional project management tools.

Dependency Types:

1. Finish-to-Start (FS): Task B cannot start until Task A finishes (most common)
2. Start-to-Start (SS): Task B cannot start until Task A starts
3. Finish-to-Finish (FF): Task B cannot finish until Task A finishes
4. Start-to-Finish (SF): Task B cannot finish until Task A starts (rare)

Implementation Details:

1. UI for Creating Links:

   • Drag-and-drop connection between tasks on Gantt chart
   • Or selection from dropdown in task properties

2. Visual Representation:

   • Arrows between dependent tasks on Gantt chart
   • Color coding for critical path
   • Visual warning for circular dependencies

3. Behavior:

   • Automatic date adjustment when linked tasks change
   • Warning when trying to schedule conflicting dates
   • Critical path calculation (sequence of dependent tasks that determine project duration)

4. Optional Enforcement:

   • Soft dependencies (visual only)
   • Hard dependencies (prevent date conflicts)

Benefits

• Realistic project workflow management
• Automatic schedule adjustments
• Critical path identification
• Prevents impossible scheduling scenarios
• Professional-grade project planning

Integration with Other Features

• Would work beautifully with Start Date feature (Issue Feature Request: Add "Start Date" field for tasks #10)
• Could integrate with resource allocation in future
• Calendar view could show dependency chains

Note: This is a more complex feature that would make Joplin's project management capabilities comparable to tools like ProjectLibre or MS Project.

This feedback was discussed with @Scrayil who suggested creating this issue.

Priority: High for professional project management users
Complexity: High - Requires new data structures, UI elements, and scheduling logic