feat: configurable OPDS download folder and filename format (#2571)

src/CrossPointSettings.h

@@ -238,6 +238,14 @@ class CrossPointSettings {
 
   // Reader screen margin settings
   uint8_t screenMargin = 5;
+  // OPDS download destination folder ("" = SD root). Global; edited from the
+  // OPDS server list. Persisted via a category-less SettingInfo::String in
+  // SettingsList.h, so it stays out of the on-device Settings screen.
+  char opdsDownloadFolder[64] = "";
+  // On-disk filename format for OPDS downloads (0=Author-Title default, 1=Title-Author,
+  // 2=Title). See OpdsFilenameFormat. Persisted via a category-less SettingInfo::Enum,
+  // edited from the OPDS server list; hidden from the on-device Settings screen.
+  uint8_t opdsFilenameFormat = 0;
   // Hide battery percentage
   uint8_t hideBatteryPercentage = HIDE_NEVER;
   // Long-press page turn button behavior