Phase 5 sub-commit 1: DevConsole + child-output capture + Ctrl+` toggle

BackendConnection now captures the bundled FrankenPHP child's merged
stdout+stderr into a 500-line ring buffer, mirrors each line through
qCInfo(lcBundled) so terminal users still see logs, and exposes
childLogTail() / childLogLine for QML.

DevConsole.qml is an opt-in monospaced viewer with auto-scroll + clear
that the skeleton and the todo example bind to Ctrl+`. Dev mode (when
BRIDGE_URL is set, no bundled child) renders an explanatory hint.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

examples/todo/qml/Main.qml

@@ -200,9 +200,22 @@ ApplicationWindow {
                     }
                 }
             }
+
+            DevConsole {
+                id: devConsole
+                visible: false
+                Layout.fillWidth: true
+                Layout.preferredHeight: 220
+            }
         }
     }
 
+    // Ctrl+`  toggles the FrankenPHP child output console (Phase 5 §13).
+    Shortcut {
+        sequences: ["Ctrl+`", "Ctrl+~"]
+        onActivated: devConsole.visible = !devConsole.visible
+    }
+
     Connections {
         target: SingleInstance
         function onLaunchArgsReceived(args) {