[Feature Request] Support RELTYPE=DEPENDS-ON

Is your feature request related to a problem? Please describe.

Failing to account for task dependencies can lead people to tackle projects in very inefficient ways.

However, there is currently no clear/obvious/standard way to indicate task dependencies in NextCloud Tasks.

This makes project planning difficult, especially in teams (or families).

Describe the solution you'd like

By supporting the RELTYPE=DEPENDS-ON parameter from RFC 9253, NextCloud Tasks would become a significantly more usable platform for planning projects. Explicit task dependencies explicit would let Nextcloud Tasks do new and useful things automatically, e.g.:

• let users filter tasks by which ones are not currently blocked (i.e. are available for progress), or vice versa
• perform critical path analysis
• generate Gantt charts
• integrate better with project planning tools such as OpenProject.

Describe alternatives you've considered

No other approaches would be standards-compliant and inter-operable.

Additional context

No response

The issue names no files, tests, or entry points. Start by reading the RFC 9253 RELTYPE=DEPENDS-ON specification, then trace how Nextcloud Tasks represents task relationships and exchanges them through its standards-based integrations. Done means dependencies are supported in an interoperable way and the requested dependency-oriented planning uses are possible.