feat(rlcd): runtime font size selector in Settings->Display

- device.properties bump default to 20
- lvgl_fonts add runtime override API (g_runtime_font_size + externs for all Montserrat sizes)
- DisplaySettings add fontSize field persisted in properties
- Display app adds Font size dropdown 14-28 applying immediately
- Lvgl.cpp applies saved runtime font on boot
- device.py new bucket <=20 includes all fonts for runtime switching (~150KB)

Co-authored-by: internal-model

Tactility/Source/settings/DisplaySettings.cpp

@@ -25,6 +25,7 @@ constexpr auto* SETTINGS_KEY_SCREENSAVER_TYPE = "screensaverType";
 constexpr auto* SETTINGS_KEY_DISABLE_WHEN_CHARGING = "disableScreensaverWhenCharging";
 constexpr auto* SETTINGS_KEY_INVERT_COLOR = "invertColor";
 constexpr auto* SETTINGS_KEY_MONO_THRESHOLD = "monochromeThreshold";
+constexpr auto* SETTINGS_KEY_FONT_SIZE = "fontSize";
 
 static Orientation getDefaultOrientation() {
     auto* display = lv_display_get_default();
@@ -187,6 +188,14 @@ bool load(DisplaySettings& settings) {
         if (mono_thresh > 255) mono_thresh = 255;
     }
 
+    int font_size = 0;
+    auto font_entry = map.find(SETTINGS_KEY_FONT_SIZE);
+    if (font_entry != map.end()) {
+        font_size = atoi(font_entry->second.c_str());
+        if (font_size < 0) font_size = 0;
+        if (font_size > 36) font_size = 36;
+    }
+
     settings.orientation = orientation;
     settings.gammaCurve = gamma_curve;
     settings.backlightDuty = backlight_duty;
@@ -196,6 +205,7 @@ bool load(DisplaySettings& settings) {
     settings.disableScreensaverWhenCharging = disable_when_charging;
     settings.invertColor = invert_color;
     settings.monochromeThreshold = static_cast<uint8_t>(mono_thresh);
+    settings.fontSize = static_cast<uint8_t>(font_size);
 
     return true;
 }
@@ -210,7 +220,8 @@ DisplaySettings getDefault() {
         .screensaverType = ScreensaverType::BouncingBalls,
         .disableScreensaverWhenCharging = false,
         .invertColor = true,
-        .monochromeThreshold = 60
+        .monochromeThreshold = 60,
+        .fontSize = 0
     };
 }
 
@@ -233,6 +244,7 @@ bool save(const DisplaySettings& settings) {
     map[SETTINGS_KEY_DISABLE_WHEN_CHARGING] = settings.disableScreensaverWhenCharging ? "1" : "0";
     map[SETTINGS_KEY_INVERT_COLOR] = settings.invertColor ? "1" : "0";
     map[SETTINGS_KEY_MONO_THRESHOLD] = std::to_string(settings.monochromeThreshold);
+    map[SETTINGS_KEY_FONT_SIZE] = std::to_string(settings.fontSize);
     auto settings_path = getSettingsFilePath();
     if (!file::findOrCreateParentDirectory(settings_path, 0755)) {
         return false;