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>

framework/skeleton/qml/Main.qml

@@ -124,6 +124,19 @@ 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
     }
 
     function _stateName(s) {