Enable public read-only project access from the Members page

Goal

Allow a project owner to make a project publicly viewable without granting visitors write access, using controls on the project Members page.

Acceptance criteria

• The Members page includes a clearly labelled control for enabling or disabling public read-only access.
• Only the project owner or an authorized administrator can change the setting.
• The page shows the project's current public-access state and explains that public visitors cannot edit it.
• When enabled, people without project membership can open the project's read-only pages without being granted member access.
• Public viewers cannot use any project mutation route, including direct HTTP/API requests.
• Disabling public access takes effect immediately without changing existing project memberships.
• Add store, handler, authorization, and UI coverage for enable, disable, public read, and rejected public writes.