Name the eye pass on the People screen

Once every image has been through the detector and only readings are
left — the state an already-indexed library is in the day the eye models
arrive — the button reads "Read eye state" rather than promising to
index, and the coverage line says what the faces are waiting for.

ui/dr-ui/src/identity_ui.rs

@@ -402,6 +402,9 @@ pub fn refresh_coverage(
             // image has a face": most of a library has none, and that is a
             // finding.
             window.set_identity_coverage_complete(a.is_complete());
+            // Detection done, readings outstanding: the button names the
+            // pass it will run rather than promising to index.
+            window.set_identity_coverage_read_only(a.coverage.is_complete() && a.unmeasured > 0);
         }
         Err(e) => {
             log::warn!("identity: coverage check: {e}");