Restructure main navigation: consolidate task system and move admin settings

[hotzenklotz]

Detailed Description

The main navigation mixes day-to-day workflow items with admin settings, and scatters task-related entries across the menu. This creates clutter and confusion — especially around the term "Projects", which is often misread by new users.

Proposed changes

• 1. Consolidate the task system
  Group Projects, Tasks, Task Types, Statistics, and Time Tracking under a single, clearly named menu section. Statistics and time tracking belong conceptually to the task system anyway, and consolidating them reduces top-level clutter. Labels should be reviewed to avoid ambiguity — especially "Projects". Administration will only cover Users, Teams, Organization Consolidate task system under a Task Management menu #9686
• 2. Move user and team administration to organization settings (long-term)
  Remove user and team management from the main menu and make it accessible via the profile icon, under an organization settings area. This keeps the main menu focused on day-to-day workflows.

Open questions

• What should the consolidated task system section be called? (e.g. "Tasks")
• Under what label should we put "Scripts"?

Context

• Specific to long-running jobs (set jobsEnabled=true in application.conf)
• Specific to webknossos.org (set isDemoInstance=true in application.conf)