Create the first Issue with a transactional team issue key

[mrboxs]

This was generated by AI during triage.

What to build

Implement Issue creation for the Core Issue Loop. A Workspace Member should be able to create an Issue from the active public Team issue list at /:workspaceSlug/team/:teamKey/active, with a required title, defaulted Workflow Status, creator attribution, and a stable Team-scoped issue key such as CORE-1.

The key behavior is transactional issue number generation through the Team Issue Counter, followed by an authoritative Issue response that refreshes the Team issue list.

Acceptance criteria

• A create Issue action is available from /:workspaceSlug/team/:teamKey/active.
• Title is required and validation errors are shown before mutation succeeds.
• Description, assignee, priority, estimate, due date, and Workflow Status are optional or defaulted.
• If no Workflow Status is selected, the Team's default Workflow Status is used.
• Issue number generation and Issue insert happen in one database transaction.
• The created Issue key uses the Team key and generated issue number.
• The signed-in user is stored as the Issue creator.
• Creating an Issue returns the authoritative record and refreshes the Team issue list.
• Concurrent Issue creation cannot produce duplicate issue numbers or issue keys.

Blocked by

• Create a Workspace and Default Team from the root page #44
• Complete the Welcome Flow and land on the active Team page #51

[linear-code]

BOXS-46