gui: finish Add URL -> File Info -> Progress dialog flow

Wires up the three dialogs from build order step 5 (docs/03-gui-spec.md
§§2-3) and the MainWindow slots that were declared but never implemented:

- AddUrlDialog: clipboard prefill is the explicit path docs/06 R2 calls
  for (no passive monitoring, not advertised).
- FileInfoDialog: async download.probe never blocks the UI; ends by
  calling download.add itself (Now / Later / Add to Queue). buildSpec()
  is a pure static so the optional-field-omission logic is unit-testable
  without touching a widget.
- ProgressDialog: non-modal, WA_DeleteOnClose, driven by the taskProgress/
  taskStateChanged signals RpcClient already re-broadcasts; download.get
  seeds state once for a dialog opened mid-transfer. Hosts SegmentBarsWidget
  and SpeedGraphWidget.

MainWindow: openAddUrlDialog/openPropertiesForSelection/showTableContextMenu
now have bodies; category.list/queue.list responses are cached so File Info
can populate its category combo and queue menu without a second round trip.
The row context menu covers what already exists (Resume/Pause/Stop/Delete/
Properties) and deliberately leaves out Open/Open With/Move-Rename/
Redownload/Add to Queue — those need dialogs later build-order steps haven't
reached yet.

util/Format.hpp: pulled the bytes/rate/eta formatting out of MainWindow and
DownloadTableModel once the dialogs wanted the same strings a third time.

Verified end-to-end against a running mockd (category.list/queue.list,
download.probe, download.add, download.get, and live event.task.progress/
event.task.state) under ASan+UBSan: all three dialogs render correctly
against real fixture data and the flow runs clean with no leaks or
sanitizer reports.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NSCdCWFXBTSBBK3MzWtJiC

gui/src/mainwindow/MainWindow.hpp

@@ -1,13 +1,16 @@
 // The main window. Lane GUI.
 //
-// M1 slice: dialogs and the tray still come later. This is the menus + toolbar + splitter
-// (category tree | table), the table driven by mockd, a status-bar connection dot, an
-// offline banner instead of a modal, and the actions that need no dialog.
+// M1 slice: the tray and the Options/Scheduler/Speed-Limiter/Batch/Grabber dialogs still
+// come later. This is the menus + toolbar + splitter (category tree | table), the table
+// driven by mockd, a status-bar connection dot, an offline banner instead of a modal, the
+// Add URL -> File Info flow, and a per-task progress dialog.
 
 #pragma once
 
 #include <QHash>
+#include <QJsonArray>
 #include <QMainWindow>
+#include <QPoint>
 
 #include "models/DownloadFilterProxy.hpp"
 #include "rpc/Protocol.hpp"
@@ -49,6 +52,10 @@ class MainWindow : public QMainWindow {
     void resumeAll();
     void pauseAll();
 
+    void openAddUrlDialog();
+    void openPropertiesForSelection();
+    void showTableContextMenu(const QPoint &pos);
+
   private:
     void buildActions();
     void buildMenus();
@@ -73,6 +80,10 @@ class MainWindow : public QMainWindow {
     QAction *actRemove_ = nullptr;
     QAction *actResumeAll_ = nullptr;
     QAction *actPauseAll_ = nullptr;
+    QAction *actProperties_ = nullptr;
+
+    QJsonArray categoriesCache_;
+    QJsonArray queuesCache_;
 
     QLabel *connDot_;
     QLabel *connText_;