fix(reader): correct slider side-button direction and legend on X3 (#2402) (#2428)

## Summary

* **What is the goal of this PR?** Fixes #2402. On the X3, the "Time to
Sleep"
picker's 5-minute side buttons were inverted (left increased, right
decreased)
  and the on-screen legend didn't match the physical buttons.
* **What changes are included?**
  * Flip the large-step (±5 min) direction on X3 so the left side button
decreases and the right increases, matching the layout. X4 is unchanged.
* Add a device-specific step-hint string
(`STR_SLEEP_TIMER_STEP_HINT_X3`)
selected via `gpio.deviceIsX3()`. X3 shows `+/-: 1 min Side buttons: 5
min`;
    X4 keeps the original `Left/Right: 1 min  Up/Down: 5 min`.
* Same fix applied to both slider pickers that read the raw up/down side
    buttons: the Time-to-Sleep picker and the "Go to %" picker
(`EpubReaderPercentSelectionActivity`), each with its own X3 hint string
    (`STR_SLEEP_TIMER_STEP_HINT_X3`, `STR_PERCENT_STEP_HINT_X3`).

## Additional Context

* **Root cause:** the X3's side buttons sit one on each edge of the
screen
(power on top), whereas the X4 has a vertical up/down rocker on the
right
edge. So `BTN_UP` is physically the *left* button on X3 but the *top*
button
  on X4. The picker mapped up→+5 / down→−5 unconditionally, which reads
naturally on the X4 rocker but inverted on the X3's left/right buttons.
The
  static legend ("Up/Down: 5 min") had the same X3-only mismatch.
* The codebase already detects the device at runtime and handles this
layout
difference elsewhere (e.g. `LyraTheme::drawSideButtonHints` draws "Up on
left,
Down on right" for X3), so this reuses the same `gpio.deviceIsX3()`
signal.
* Swept the codebase for other side-button sliders:
`ClockOffsetActivity` already
uses the `Next/Previous` (`ButtonNavigator`) abstraction, which resolves
to
left=decrement / right=increment on X3, so it needs no change. List/page
navigation (Wi-Fi, KOReader sync, BMP viewer) and the keyboard cursor
are also
unaffected. The two slider pickers above were the only ones using raw
up/down.
* **X4 is untouched** — same direction, same legend wording as before.
* **Tested on X3 hardware:** left side button now decreases, right
increases, and
  the legend matches. X4 not yet tested on device (no unit on hand); its
  behaviour and strings are unchanged from master.
* **Translations:** the new `STR_SLEEP_TIMER_STEP_HINT_X3` and
`STR_PERCENT_STEP_HINT_X3` were added to all 26 languages, but the
non-English
  ones are AI-generated and would benefit from a native-speaker pass —
particularly Hebrew (RTL ordering with a leading `+/-`), Kazakh, and
Vietnamese.

---

### AI Usage

Did you use AI tools to help write this code? _**YES**_

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/activities/util/IntervalSelectionActivity.cpp

@@ -1,6 +1,7 @@
 #include "IntervalSelectionActivity.h"
 
 #include <GfxRenderer.h>
+#include <HalGPIO.h>
 #include <I18n.h>
 
 #include <algorithm>
@@ -25,6 +26,18 @@ void IntervalSelectionActivity::adjustValue(const int delta) {
   requestUpdate();
 }
 
+void IntervalSelectionActivity::drawStepHintLine(const int y, const StrId labelId, const int step) {
+  char stepText[24];
+  if (valueFormatId != StrId::STR_NONE_OPT) {
+    snprintf(stepText, sizeof(stepText), I18N.get(valueFormatId), static_cast<unsigned int>(step));
+  } else {
+    snprintf(stepText, sizeof(stepText), "%d", step);
+  }
+  char line[64];
+  snprintf(line, sizeof(line), "%s %s", I18N.get(labelId), stepText);
+  renderer.drawCenteredText(SMALL_FONT_ID, y, line, true);
+}
+
 void IntervalSelectionActivity::loop() {
   if (ignoreConfirmRelease) {
     if (mappedInput.wasReleased(MappedInputManager::Button::Confirm)) {
@@ -52,8 +65,15 @@ void IntervalSelectionActivity::loop() {
 
   buttonNavigator.onPressAndContinuous({MappedInputManager::Button::Left}, [this] { adjustValue(-smallStep); });
   buttonNavigator.onPressAndContinuous({MappedInputManager::Button::Right}, [this] { adjustValue(smallStep); });
-  buttonNavigator.onPressAndContinuous({MappedInputManager::Button::Up}, [this] { adjustValue(largeStep); });
-  buttonNavigator.onPressAndContinuous({MappedInputManager::Button::Down}, [this] { adjustValue(-largeStep); });
+
+  // On X3 the side buttons sit on the left/right edges of the screen rather than as a vertical up/down
+  // rocker (X4), so BTN_UP is physically the left button and BTN_DOWN the right one. Flip the large-step
+  // direction there so the left button decreases and the right button increases, matching the layout.
+  const int upDelta = gpio.deviceIsX3() ? -largeStep : largeStep;
+  const int downDelta = gpio.deviceIsX3() ? largeStep : -largeStep;
+  buttonNavigator.onPressAndContinuous({MappedInputManager::Button::Up}, [this, upDelta] { adjustValue(upDelta); });
+  buttonNavigator.onPressAndContinuous({MappedInputManager::Button::Down},
+                                       [this, downDelta] { adjustValue(downDelta); });
 }
 
 void IntervalSelectionActivity::render(RenderLock&&) {
@@ -88,7 +108,11 @@ void IntervalSelectionActivity::render(RenderLock&&) {
   const int knobX = std::max(barX + 2, barX + 2 + fillWidth - 2);
   renderer.fillRect(knobX, barY - 4, 4, barHeight + 8, true);
 
-  renderer.drawCenteredText(SMALL_FONT_ID, barY + 30, I18N.get(stepHintId), true);
+  // Two-line step hint: front buttons do the small step, side buttons the large step. Built from
+  // separate label + value strings (rather than splitting one localized sentence) so the layout
+  // doesn't depend on translators preserving a hidden separator.
+  drawStepHintLine(barY + 30, StrId::STR_STEP_HINT_FRONT, smallStep);
+  drawStepHintLine(barY + 52, StrId::STR_STEP_HINT_SIDE, largeStep);
 
   const auto labels = mappedInput.mapLabels(tr(STR_BACK), tr(STR_SELECT), "-", "+");
   GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);

src/activities/util/IntervalSelectionActivity.h

@@ -11,13 +11,12 @@ class GfxRenderer;
 class IntervalSelectionActivity final : public Activity {
  public:
   explicit IntervalSelectionActivity(GfxRenderer& renderer, MappedInputManager& mappedInput, const char* activityName,
-                                     StrId titleId, StrId stepHintId, int initialValue, int minValue, int maxValue,
-                                     int smallStep, int largeStep, StrId valueFormatId = StrId::STR_NONE_OPT,
+                                     StrId titleId, int initialValue, int minValue, int maxValue, int smallStep,
+                                     int largeStep, StrId valueFormatId = StrId::STR_NONE_OPT,
                                      bool readerActivity = false, bool ignoreInitialConfirmRelease = false,
                                      StrId maxBoundaryLabelId = StrId::STR_NONE_OPT)
       : Activity(activityName, renderer, mappedInput),
         titleId(titleId),
-        stepHintId(stepHintId),
         valueFormatId(valueFormatId),
         maxBoundaryLabelId(maxBoundaryLabelId),
         value(initialValue),
@@ -35,7 +34,6 @@ class IntervalSelectionActivity final : public Activity {
 
  private:
   StrId titleId;
-  StrId stepHintId;
   StrId valueFormatId;
   StrId maxBoundaryLabelId;
   int value;
@@ -49,4 +47,5 @@ class IntervalSelectionActivity final : public Activity {
 
   void adjustValue(int delta);
   int clampedValue(int candidate) const;
+  void drawStepHintLine(int y, StrId labelId, int step);
 };