Onboarding tour URL parameter start_onboarding_tour=true leads to 404 / page not found in OpenProject 17.0.2

Description
When a new user is created in OpenProject 17, the application offers an onboarding tour.
However, when the tour is triggered via the URL parameter start_onboarding_tour=true, the target page results in a 404 – Page not found error.

Example URL:
/projects//work_packages?start_onboarding_tour=true

Instead of starting the onboarding tour, the application reports that the page cannot be found.

Expected behavior

• The onboarding tour should start automatically when start_onboarding_tour=true is present in the URL
• Alternatively, the parameter should be ignored gracefully without breaking page routing

Actual behavior

• The work packages page is not found
• The user is blocked from accessing the project context
• Onboarding cannot be completed

Environment

• OpenProject version: 17.0.2
• Deployment type: self-hosted
• Browser: Chrome on MacOS
• User type: newly created user (first login)

Additional context

• The codebase contains onboarding-related routes and components, but the query parameter start_onboarding_tour does not seem to be handled correctly at routing or controller level
• It is unclear whether this parameter was deprecated, renamed, or never fully implemented in the current UI architecture

Questions for maintainers

• Is start_onboarding_tour=true still a supported mechanism in OpenProject 17?
• Has the onboarding tour entry point been moved or refactored?
• Should this parameter be removed, redirected, or fixed?

Impact
This issue affects first-time user experience and may cause confusion during onboarding, especially in enterprise or customer-facing deployments.

Start by reproducing the reported /projects//work_packages?start_onboarding_tour=true URL in OpenProject 17.0.2, then inspect the onboarding-related routes, controllers, and components mentioned in the issue. Done means the work packages page loads and the onboarding tour starts, or the parameter is ignored without causing a 404.