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/ui/identity.slint

@@ -270,6 +270,12 @@ export component IdentityScreen inherits Rectangle {
     // hides the reason the rest are outstanding.
     in property <string> coverage;
     in property <bool> coverage-complete: false;
+    /// TRACES: FR-CULL-8a
+    /// Every image has been through the detector and only faces are left to
+    /// read — the eye pass over a library indexed before the eye models
+    /// existed. The same sweep, fetching the same originals; the button says
+    /// what it will actually do.
+    in property <bool> coverage-read-only: false;
     // No model on disk: face indexing cannot run at all (docs/faces.md §2.2).
     in property <bool> model-missing: false;
     in property <int> picked-count: 0;
@@ -616,7 +622,7 @@ export component IdentityScreen inherits Rectangle {
                     clicked => { root.confirm-all(); }
                 }
                 if !root.indexing && !root.model-missing && !root.coverage-complete: Button {
-                    text: "Index faces";
+                    text: root.coverage-read-only ? "Read eye state" : "Index faces";
                     clicked => { root.index-faces(); }
                 }
                 if root.indexing: Button {