gui: RPC client, download table model, and a live main window

First vertical slice of velox-gui, built entirely against tools/mockd
(no daemon dependency):

- rpc/: RpcConnection runs a QLocalSocket on a worker thread with
  newline-delimited JSON-RPC framing, drives the session.hello /
  session.subscribe handshake, and reconnects with exponential backoff
  (250 ms -> 8 s). RpcClient is the main-thread face: marshals calls onto
  the worker, delivers replies as main-thread callbacks, re-emits server
  notifications as typed Qt signals, and issues the one-shot download.list
  on reaching Connected.
- models/DownloadTableModel: QAbstractTableModel over TaskSummary. A
  progress batch is a row patch with a narrow dataChanged over the value
  columns only; beginResetModel() is reserved for the initial load and a
  reconnect resync.
- widgets/ProgressDelegate: in-cell progress bar for the Status column.
- mainwindow/MainWindow: the table, a status-bar connection dot, an
  offline banner instead of a modal, dialog-free pause/resume/stop
  actions, and QSettings column/geometry persistence.
- gui/CMakeLists.txt links velox::proto (never velox::core, ADR 0009) and
  self-guards on the veloxproto target so main keeps configuring if it is
  ever absent again.
- i18n from the first commit: every string via tr(), plus an Arabic .ts
  stub for the RTL check.
- tests/: headless QTest for the model — proves the progress patch is a
  narrow dataChanged and never resets the model.

Verified end-to-end against `mockd --tasks 300`: handshake, initial list,
live progress batches applied to the model, and a clean
Reconnecting -> Connected recovery when mockd is bounced mid-run.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_016Ne28kx4VreeBWZv82Nksd

gui/src/widgets/ProgressDelegate.cpp

@@ -0,0 +1,44 @@
+#include "widgets/ProgressDelegate.hpp"
+
+#include <QApplication>
+#include <QPainter>
+#include <QStyleOptionProgressBar>
+
+#include "models/DownloadTableModel.hpp"
+
+namespace velox::gui {
+
+void ProgressDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option,
+                             const QModelIndex &index) const {
+    const QVariant progressVar = index.data(DownloadTableModel::ProgressRole);
+    const double progress = progressVar.isValid() ? progressVar.toDouble() : -1.0;
+
+    if (progress < 0.0) {
+        QStyledItemDelegate::paint(painter, option, index);
+        return;
+    }
+
+    QStyleOptionViewItem opt(option);
+    initStyleOption(&opt, index);
+    // We draw the bar ourselves; suppress the default text so it is not painted twice.
+    opt.text.clear();
+    QStyle *style = opt.widget ? opt.widget->style() : QApplication::style();
+    style->drawControl(QStyle::CE_ItemViewItem, &opt, painter, opt.widget);
+
+    QStyleOptionProgressBar bar;
+    bar.state = option.state | QStyle::State_Horizontal;
+    bar.direction = option.direction;
+    bar.rect = option.rect.adjusted(3, 3, -3, -3);
+    bar.fontMetrics = option.fontMetrics;
+    bar.palette = option.palette;
+    bar.minimum = 0;
+    bar.maximum = 10000;
+    bar.progress = static_cast<int>(progress * 10000.0);
+    bar.textVisible = true;
+    bar.textAlignment = Qt::AlignCenter;
+    bar.text = index.data(Qt::DisplayRole).toString();
+
+    style->drawControl(QStyle::CE_ProgressBar, &bar, painter, opt.widget);
+}
+
+}  // namespace velox::gui

gui/src/widgets/ProgressDelegate.hpp

@@ -0,0 +1,23 @@
+// In-cell progress bar for the Status column. Lane GUI.
+//
+// docs/03-gui-spec.md §1: "Progress bar drawn by a QStyledItemDelegate in the Status
+// column." Reads DownloadTableModel::ProgressRole; falls back to plain text for rows with
+// no measurable progress (unknown size, or a non-downloading state).
+
+#pragma once
+
+#include <QStyledItemDelegate>
+
+namespace velox::gui {
+
+class ProgressDelegate : public QStyledItemDelegate {
+    Q_OBJECT
+
+  public:
+    using QStyledItemDelegate::QStyledItemDelegate;
+
+    void paint(QPainter *painter, const QStyleOptionViewItem &option,
+               const QModelIndex &index) const override;
+};
+
+}  // namespace velox::gui