Edit core Issue properties from detail

[mrboxs]

This was generated by AI during triage.

What to build

Implement core Issue editing for the Core Issue Loop. From Issue detail at /:workspaceSlug/team/:teamKey/issues/$issueKey, a Workspace Member should be able to update the fields that make an Issue operational: title, plain description, Workflow Status, assignee, priority, estimate, and due date.

The server should validate Team/Workspace ownership for every referenced value and return the authoritative updated Issue so the active Team issue list and Issue detail views stay consistent.

Acceptance criteria

• A Workspace Member can update Issue title from the detail route.
• A Workspace Member can update a plain description representation from the detail route.
• A Workspace Member can update Workflow Status, assignee, priority, estimate, and due date.
• Status changes can only target Workflow Statuses belonging to the Issue's Team.
• Assignee changes can only target Workspace Members in the same Workspace.
• Moving an Issue into a Started, Completed, or Canceled status category updates startedAt, completedAt, or canceledAt consistently.
• Moving an Issue out of Completed clears completedAt.
• Moving an Issue out of Canceled clears canceledAt.
• Mutations return authoritative records and refresh /:workspaceSlug/team/:teamKey/active and Issue detail state through TanStack Query invalidation.
• Invalid updates return structured validation, forbidden, not found, or conflict errors as appropriate.

Blocked by

• Create the first Issue with a transactional team issue key #45
• Open an Issue through its canonical Team route #46

[linear-code]

BOXS-48