[RED] Capture failing tests for route and slot plugin contributions

[ksamaschke]

Phase

RED

## Deliverable
Create failing tests that assert plugin UI contributions register against routes, slots, and settings sections rather than dashboard tabs.

## Dependencies
- Parent work item: #218.

• Blocked by Work Item: Replace tab navigation with persistent sidebar routes #215.

  Completion evidence

  • Failing tests naming route-panel, toolbar-action, detail-pane, or settings-section contribution points.

• Coverage references for tab-based contribution removal or compatibility shims.

  Acceptance criteria

  • Tests fail while the plugin runtime remains tab-centric.

• Expected plugin extension points are precise enough for implementation.

  Parent: Work Item: Migrate plugin contributions from tabs to route and slot APIs #218