fix(desktop): make user delete work, refetch every panel on a project change

[pyramation]

Summary

Delete did nothing because the button was disabled. The Users tab blocked removal for the only admin — which, in a one-user project, is the only row there is. The store's rule is narrower: losing the last admin is only a lock-out while other users remain; removing the very last account is allowed (it just disables UI logins, and is undone by adding a user). The two rules now come from one place:

userRemovalBlock(users, target) // null = allowed, otherwise the reason (shown as the button's title)
  target.role !== 'admin'      → null
  users.length <= 1            → null           // ← the case the UI got wrong
  admins <= 1                  → 'The last admin cannot be removed while other users exist.'

roleChangeBlock(users, target, next)  // demoting the only admin stays blocked, always

And a refused write is no longer invisible: every runAction(...) failure lands in a dismissible banner, where before void withBusy(...) turned a store rejection into an unhandled promise rejection and a button that looked dead.

Panels kept mount-time data. Each project-scoped hook refetched on the project name, so nothing refetched when the contents changed underneath the same name — switching the project in use, importing over a project, clear-all:

-useProjectUsers(project: string | null)
+useProjectUsers({ project, rev }: ProjectScope)
   const refresh = useCallback(…, [project, rev]);

App holds one dataRev and hands out activeScope / editingScope, bumping it on use / create / remove / import / clear. That's the general version of the fix in #92, which only cleared the pinned config project and restarted the brain.

Link to Devin session: https://app.devin.ai/sessions/972698f89f494b86828010666a002b8f
Requested by: @pyramation

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