[Test] Build Assignment Atlas route with owner clusters

[iamasx]

Summary

Build an assignment-atlas route with owner clusters, task cards, and a compact allocation summary rail.

Scope

• Add a new assignment-atlas route.
• Create mock owner, task, and allocation data.
• Build cluster sections, task cards, and a summary rail.
• Aim for roughly 400-500 changed lines overall, staying reasonably close to that range.

Acceptance Criteria

• The route shows owner clusters and task content.
• Allocation details are visible.
• The layout remains usable across common breakpoints.
• Tests cover the key render paths.

[iamasx]

Implementation plan:

• Add the assignment-atlas route shell and supporting mock data.
• Build owner cluster, task card, and allocation summary components.
• Assemble the page with a clear grouping structure and responsive behavior.
• Add visual polish and route tests.