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/qml/src/BackendConnection.h

@@ -3,7 +3,9 @@
 #include <QElapsedTimer>
 #include <QObject>
 #include <QProcess>
+#include <QQueue>
 #include <QString>
+#include <QStringList>
 #include <QtQmlIntegration>
 
 class QNetworkAccessManager;
@@ -78,6 +80,11 @@ public:
     /// after this completes; emits `updateApplied` / `updateApplyFailed`.
     Q_INVOKABLE void applyUpdate();
 
+    /// Returns a snapshot of the captured child stdout/stderr ring buffer
+    /// (most recent kChildLogMax lines). Bundled mode only — empty in dev
+    /// mode. Used by `DevConsole.qml` to seed its view on first show.
+    Q_INVOKABLE QStringList childLogTail() const;
+
 signals:
     void urlChanged();
     void tokenChanged();
@@ -94,10 +101,16 @@ signals:
     void updateApplied();
     void updateApplyFailed(const QString& reason);
 
+    /// Emitted for each newline-terminated chunk read from the bundled
+    /// FrankenPHP child's merged stdout+stderr stream. DevConsole.qml
+    /// listens for these to populate its log view live.
+    void childLogLine(const QString& line);
+
 private slots:
     void probe();
     void onProbeFinished();
     void onChildFinished(int exitCode, QProcess::ExitStatus status);
+    void onChildOutputReady();
     void onUpdateCheckFinished(int exitCode, QProcess::ExitStatus status);
     void onUpdateApplyFinished(int exitCode, QProcess::ExitStatus status);
 
@@ -138,6 +151,10 @@ private:
     int m_supervisorRetries = 0;
     static constexpr int kMaxSupervisorRetries = 5;
 
+    QQueue<QString> m_childLog;
+    QString m_childLogBuffer;
+    static constexpr int kChildLogMax = 500;
+
     QProcess* m_updateCheck = nullptr;
     QProcess* m_updateApply = nullptr;