Make the Identity Manager a peer of the library and develop

It was reachable only from the library header, which made it a side trip
rather than a mode. It is now reachable from develop's header too, beside
the way back, because that is the same kind of move -- leaving this
photograph for somewhere else in the library -- and a screen you can only
reach from one of the other two is not a peer of them.

Leaving returns to whichever screen opened it, and the button says which.
A back button that read "Library" while returning to develop would be
lying about the one thing a back button has to be right about. The
develop session is only hidden, never torn down, so returning to it costs
nothing and keeps the photographer's place.

The header now matches the other two screens rather than using a close
cross: three screens whose headers disagree read as three applications.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/dr-ui/ui/app.slint

@@ -46,6 +46,7 @@ component StatusBar inherits Rectangle {
     in property <bool> can-redo: false;
 
     callback back-to-library();
+    callback open-people();
     callback open-settings();
     callback toggle-panel();
     callback export-image();
@@ -99,6 +100,18 @@ component StatusBar inherits Rectangle {
             clicked => { root.back-to-library(); }
         }
 
+        // The third screen, reachable from the second. Beside the way back
+        // because it is the same kind of move — leaving this photograph for
+        // somewhere else in the library — and because a mode you can only
+        // reach from one of the other two is not a peer of them, whatever the
+        // navigation model says.
+        Button {
+            text: "Identity";
+            y: (parent.height - self.height) / 2;
+            visible: root.can-return-to-library;
+            clicked => { root.open-people(); }
+        }
+
         Value { text: root.filename; compact: true; overflow: elide; }
 
         Caption { text: root.position; }
@@ -534,6 +547,7 @@ export component AppWindow inherits Window {
     in property <bool> identity-indexing: false;
     in property <string> identity-indexing-status;
     in property <bool> identity-model-missing: false;
+    in property <string> identity-back-label: "‹ Library";
     in property <string> identity-coverage;
     in property <bool> identity-coverage-complete: false;
     in property <int> identity-picked: 0;
@@ -1287,6 +1301,7 @@ in property <bool> panel-visible: true;
             indexing-status: root.identity-indexing-status;
             model-missing: root.identity-model-missing;
             picked-count: root.identity-picked;
+            back-label: root.identity-back-label;
             coverage: root.identity-coverage;
             coverage-complete: root.identity-coverage-complete;
 
@@ -1578,6 +1593,7 @@ in property <bool> panel-visible: true;
                 can-undo: root.can-undo;
                 can-redo: root.can-redo;
                 back-to-library() => { root.back-to-library(); }
+                open-people() => { root.identity-open(); }
                 open-settings() => { root.settings-open(); }
                 toggle-panel() => { root.toggle-panel(); }
                 export-image() => { root.export-image(); }