Add colab button got win 3.1 style

[wilhel1812]

Edit
Got an old school UI style looking like it came from Windows 3.1.

[wilhel1812]

Starting combined 0.19.0 quick-polish batch with #771 on branch issue/771-773-quick-polish, per current-thread approval to reduce deploy churn. Scope: replace the existing Edit collaborators trigger styling with the documented button system while preserving the current popover behavior. Drift check before coding shows only known 0.18.0 squash-policy drift tracked by #780.

[wilhel1812]

Implemented in PR #789 and deployed to shared staging. Staging commit: 21bdb3d. Build label from deploy logs: 0.18.0+21bdb3dd. Verification before merge: targeted tests, full npm test, and npm run build all passed. Awaiting staging sign-off before closure.

[wilhel1812]

Reopening for staging follow-up: another collaborator remove control still uses the legacy inline-action inline-action-icon access-collaborator-remove button styling and should move to the documented button system like the earlier #773 fix. Drift check before coding shows only the known 0.18.0 squash-policy drift tracked by #780.