feat: add OPDS server reordering with sortOrder field and numeric stepper

Servers are sorted by a persistent sortOrder field (ties broken
alphabetically). On-device editing uses a new NumericStepperActivity
with side buttons for ±1 and face buttons for ±10. The web UI gets
up/down arrow buttons and a POST /api/opds/reorder endpoint.

Made-with: Cursor

src/activities/util/NumericStepperActivity.cpp

@@ -0,0 +1,99 @@
+#include "NumericStepperActivity.h"
+
+#include <GfxRenderer.h>
+#include <I18n.h>
+
+#include <algorithm>
+#include <cstdio>
+
+#include "MappedInputManager.h"
+#include "components/UITheme.h"
+#include "fontIds.h"
+
+void NumericStepperActivity::onEnter() {
+  Activity::onEnter();
+  requestUpdate();
+}
+
+void NumericStepperActivity::onExit() { Activity::onExit(); }
+
+void NumericStepperActivity::loop() {
+  if (mappedInput.wasPressed(MappedInputManager::Button::Back)) {
+    if (onCancel) onCancel();
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Confirm)) {
+    if (onComplete) onComplete(value);
+    return;
+  }
+
+  // Side buttons: ±1
+  if (mappedInput.wasPressed(MappedInputManager::Button::Up)) {
+    if (value < maxValue) {
+      value++;
+      requestUpdate();
+    }
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Down)) {
+    if (value > minValue) {
+      value--;
+      requestUpdate();
+    }
+    return;
+  }
+
+  // Front face buttons: ±10
+  if (mappedInput.wasPressed(MappedInputManager::Button::Right)) {
+    value = std::min(value + 10, maxValue);
+    requestUpdate();
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Left)) {
+    value = std::max(value - 10, minValue);
+    requestUpdate();
+    return;
+  }
+}
+
+void NumericStepperActivity::render(Activity::RenderLock&&) {
+  renderer.clearScreen();
+
+  const auto pageWidth = renderer.getScreenWidth();
+  const int lineHeight12 = renderer.getLineHeight(UI_12_FONT_ID);
+
+  const auto& metrics = UITheme::getInstance().getMetrics();
+  GUI.drawHeader(renderer, Rect{0, metrics.topPadding, pageWidth, metrics.headerHeight}, title.c_str());
+
+  char valueStr[16];
+  snprintf(valueStr, sizeof(valueStr), "%d", value);
+
+  const int textWidth = renderer.getTextWidth(UI_12_FONT_ID, valueStr);
+  const int startX = (pageWidth - textWidth) / 2;
+  const int valueY = metrics.topPadding + metrics.headerHeight + 60;
+
+  constexpr int highlightPad = 10;
+  renderer.fillRoundedRect(startX - highlightPad, valueY - 4, textWidth + highlightPad * 2, lineHeight12 + 8, 6,
+                           Color::LightGray);
+  renderer.drawText(UI_12_FONT_ID, startX, valueY, valueStr, true);
+
+  const int arrowX = pageWidth / 2;
+  const int arrowUpY = valueY - 20;
+  const int arrowDownY = valueY + lineHeight12 + 12;
+  constexpr int arrowSize = 6;
+  for (int row = 0; row < arrowSize; row++) {
+    renderer.drawLine(arrowX - row, arrowUpY + row, arrowX + row, arrowUpY + row);
+  }
+  for (int row = 0; row < arrowSize; row++) {
+    renderer.drawLine(arrowX - row, arrowDownY + arrowSize - 1 - row, arrowX + row, arrowDownY + arrowSize - 1 - row);
+  }
+
+  const auto labels = mappedInput.mapLabels(tr(STR_BACK), tr(STR_SAVE), "-10", "+10");
+  GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+  GUI.drawSideButtonHints(renderer, "+1", "-1");
+
+  renderer.displayBuffer();
+}

src/activities/util/NumericStepperActivity.h

@@ -0,0 +1,42 @@
+#pragma once
+
+#include <functional>
+#include <string>
+#include <utility>
+
+#include "activities/Activity.h"
+
+/**
+ * Reusable numeric stepper for integer value entry.
+ * Side buttons (Up/Down) step by 1, face buttons (Left/Right) step by 10.
+ * Value is clamped within [min, max].
+ */
+class NumericStepperActivity final : public Activity {
+ public:
+  using OnCompleteCallback = std::function<void(int)>;
+  using OnCancelCallback = std::function<void()>;
+
+  explicit NumericStepperActivity(GfxRenderer& renderer, MappedInputManager& mappedInput, std::string title,
+                                  int initialValue, int minValue, int maxValue, OnCompleteCallback onComplete,
+                                  OnCancelCallback onCancel)
+      : Activity("NumericStepper", renderer, mappedInput),
+        title(std::move(title)),
+        value(initialValue),
+        minValue(minValue),
+        maxValue(maxValue),
+        onComplete(std::move(onComplete)),
+        onCancel(std::move(onCancel)) {}
+
+  void onEnter() override;
+  void onExit() override;
+  void loop() override;
+  void render(Activity::RenderLock&&) override;
+
+ private:
+  std::string title;
+  int value;
+  int minValue;
+  int maxValue;
+  OnCompleteCallback onComplete;
+  OnCancelCallback onCancel;
+};