[Oracle/Client] Report card database download progress

Card database updates ran invisibly: MTGJSON parsing spun an indeterminate
bar on the UI thread and the set import blocked the window, while the
onboarding wizard spawned `oracle -b` with no progress to show at all.

- Add byte-level scan progress to `RawJson::scanSetRanges` via an optional
  callback, throttled to ~100 reports per scan.
- Emit `OracleImporter::dataReadProgress` during the scan and import sets on a
  worker thread, driving the wizard's progress bar per set.
- With `-b`, write machine-readable `PROGRESS <stage> <done> <total>` lines to
  stdout for the download/scan/import stages; stderr keeps the log output.
- Parse the oracle stdout in `MainWindow` and forward it to the onboarding
  wizard, giving the card database step a determinate bar with stage-specific
  status text.
- Guard the async workers against the wizard being closed mid-run.
- Add Google Test coverage for scan progress reporting.

oracle/src/pages.h

@@ -83,13 +83,14 @@ private:
 
     QFutureWatcher<bool> watcher;
     QFuture<bool> future;
-    QByteArray jsonData;
 
 private slots:
     void actLoadSetsFile();
     void actRestoreDefaultUrl();
     void actDownloadProgressSetsFile(qint64 received, qint64 total);
     void actDownloadFinishedSetsFile();
+    void updateParsingProgress(int bytesRead, int totalBytes);
+    void scanProgressToStdout(int bytesRead, int totalBytes);
     void importFinished();
     void zipDownloadFailed(const QString &message);
 };
@@ -103,16 +104,21 @@ public:
 
 private:
     QTextEdit *messageLog;
+    QProgressBar *progressBar;
     QCheckBox *defaultPathCheckBox;
     QLabel *pathLabel;
     QLabel *saveLabel;
 
+    QFutureWatcher<int> importWatcher;
+    QFuture<int> importFuture;
+
 protected:
     void initializePage() override;
     void cleanupPage() override;
     bool validatePage() override;
 
 private slots:
+    void importFinished();
     void updateTotalProgress(int cardsImported, int setIndex, const QString &setName);
 };