Slice 7: Add internal auth and workspace scoping if distribution expands

[newbish]

Objective

Protect the app if it grows beyond a tiny internal audience.

Tasks

• Decide whether network-level restriction is enough
• If not, add auth middleware appropriate for Workers
• Add workspace scoping if multiple teams will use the app
• Add audit logging for admin changes if config becomes mutable

Acceptance criteria

• Access model is documented
• Auth and scoping are only added if the distribution model requires them

Note

Do not front-load auth complexity if the audience is still small and internal.