Rework scrum project feature guards as routing constraints

[myabc]

Important

This PR is based off #22086. Please review/merge that PR first.

Ticket

n/a

What are you trying to accomplish?

Use Constraints::FeatureDecision for the scrum-only sprint and backlog sharing routes, and move the inactive-flag expectations from controller specs into routing specs.

What approach did you choose and why?

routing constraints are a cleaner and more concise way of adding guards for functionality behind feature flags

Merge checklist

• Added/updated tests
• Tested major browsers (Chrome, Firefox, Edge, ...)

[Copilot]

Pull request overview

This PR moves scrum_projects feature-flag gating for the Backlogs “new Agile sprint” endpoints and backlog sharing settings from controller-level checks to route-level constraints, and updates specs accordingly.

Changes:

• Wrap new sprint-related routes and backlog sharing settings routes in Constraints::FeatureDecision.new(:scrum_projects).
• Remove controller-level feature flag guards that are now redundant due to routing constraints.
• Update/add routing specs to assert routes are (not) available depending on the flag.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
modules/backlogs/config/routes.rb	Gates new sprint + backlog sharing settings routes behind scrum_projects routing constraint.
modules/backlogs/app/controllers/rb_sprints_controller.rb	Removes feature-flag authorization checks now handled by routing.
modules/backlogs/app/controllers/projects/settings/backlog_sharings_controller.rb	Removes feature-flag 404 guard now handled by routing.
modules/backlogs/spec/routing/rb_sprints_routing_spec.rb	Adds routing expectations for flag active/inactive cases.
modules/backlogs/spec/routing/rb_stories_routing_spec.rb	Adds routing expectations for the flagged move route.
modules/backlogs/spec/routing/projects/settings/backlog_sharings_routing_spec.rb	New routing spec covering backlog sharing settings routes under the flag.
modules/backlogs/spec/controllers/rb_sprints_controller_spec.rb	Removes “flag inactive” controller examples (now unroutable).
modules/backlogs/spec/controllers/projects/settings/backlog_sharings_controller_spec.rb	Removes “flag inactive” controller examples (now unroutable).
modules/backlogs/spec/features/projects/settings/backlog_sharing_settings_spec.rb	Drops direct-access 404 assertion when the flag is inactive.

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