A nav item says which permission its page needs

The sidebar hides what the caller cannot reach - that is what makes it useful
to a guest, and what stops a member with a sparse role being offered links that
can only answer 403. It reads the permission off the nav item to decide.

Only four items ever declared one. Machines, PCs, Printers, Network, USB,
Knowledge Base, Notifications, Calendar, Dashboard, Map, Applications and
Reports declared nothing, so the filter had nothing to go on: granting the
guest role machines.view opened the API and left the sidebar empty, which reads
as the grant not working.

Every item now names its read permission - in the plugins, in the core
navigation endpoint, and in the frontend's fallback list, which is what renders
when the endpoint is unreachable and would otherwise disagree with it.

CHANGELOG.md

@@ -115,6 +115,15 @@ ADR-007 and ADR-002.
 
 ### Fixed
 
+- **The sidebar offered pages the reader could not open, and hid ones they
+  could.** A nav item is hidden from anybody who does not hold its permission,
+  but only four items ever declared one - so the filter did nothing for the
+  rest, and a signed-out visitor granted `machines.view` still saw an empty
+  sidebar. Every item now names the read permission its page needs, in the
+  plugins, in the core navigation endpoint and in the frontend's fallback list.
+  A signed-in member with a sparse role will notice the same correction: a link
+  that could only answer 403 no longer appears.
+
 - **Every report offers to email itself, not just two of them.** `POST
   /api/reports/email` has always taken any `{columns, rows}`, but the button was
   on the toner and warranty pages only - because those two happen to be their