feat: add Zammad ticket observability

[Optic00]

Summary

• Add a workspace dashboard widget with ticket counts, status distribution, linked-ticket rows, and direct links to Zammad.
• Record status, group, and owner changes observed during Windshift synchronization and show recent changes both in the workspace overview and on the linked item.
• Refine the item sidebar card with ticket title, group, owner, sync time, status colors, refresh/edit/unlink actions, and clearer synchronization states.

Stack

This PR is stacked on Windshiftapp#238 and contains only the observability and UI follow-up. It is opened in the contributor fork so the review diff excludes the core integration commits. It should be reviewed after the core integration and not merged into the base branch first. Once Windshiftapp#238 is merged, this branch will be rebased onto upstream main and submitted there.

Validation

• go test ./...
• Frontend, from frontend/:
  • npm run check
  • npm run typecheck
  • npm run test:run
  • npm run build
• Manual UI validation against a private Zammad/Windshift lab installation

This has not been exercised in production.

[github-actions]

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