feat: A web editor for settings (#667)

## Summary

This is an updated version of @itsthisjustin's #346 that builds on
current master and also deduplicates the settings list so we don't have
two copies of the settings. In the Web UI, it should organize the
settings a little closer to what you see on device.

## Additional Context

I tested this live on device and it seems to play nicely for me. It's
re-based on master since master's settings stuff has moved somewhat
since the original PR and addresses the sole review comment #346 - it
also means that I don't need to manually key in the URL for my OPDS
server. :)

---

### AI Usage

My changes were implemented with Claude Opus 4.5 and Claude Code 2.1.25.
I don't know if @itsthisjustin's original work used AI assistance.

Co-authored-by: Dave Allie <dave@daveallie.com>

src/activities/settings/SettingsActivity.h

@@ -11,12 +11,12 @@
 
 class CrossPointSettings;
 
-enum class SettingType { TOGGLE, ENUM, ACTION, VALUE };
+enum class SettingType { TOGGLE, ENUM, ACTION, VALUE, STRING };
 
 struct SettingInfo {
   const char* name;
   SettingType type;
-  uint8_t CrossPointSettings::* valuePtr;
+  uint8_t CrossPointSettings::* valuePtr = nullptr;
   std::vector<std::string> enumValues;
 
   struct ValueRange {
@@ -24,20 +24,100 @@ struct SettingInfo {
     uint8_t max;
     uint8_t step;
   };
-  ValueRange valueRange;
+  ValueRange valueRange = {};
 
-  static SettingInfo Toggle(const char* name, uint8_t CrossPointSettings::* ptr) {
-    return {name, SettingType::TOGGLE, ptr};
+  const char* key = nullptr;       // JSON API key (nullptr for ACTION types)
+  const char* category = nullptr;  // Category for web UI grouping
+
+  // Direct char[] string fields (for settings stored in CrossPointSettings)
+  char* stringPtr = nullptr;
+  size_t stringMaxLen = 0;
+
+  // Dynamic accessors (for settings stored outside CrossPointSettings, e.g. KOReaderCredentialStore)
+  std::function<uint8_t()> valueGetter;
+  std::function<void(uint8_t)> valueSetter;
+  std::function<std::string()> stringGetter;
+  std::function<void(const std::string&)> stringSetter;
+
+  static SettingInfo Toggle(const char* name, uint8_t CrossPointSettings::* ptr, const char* key = nullptr,
+                            const char* category = nullptr) {
+    SettingInfo s;
+    s.name = name;
+    s.type = SettingType::TOGGLE;
+    s.valuePtr = ptr;
+    s.key = key;
+    s.category = category;
+    return s;
   }
 
-  static SettingInfo Enum(const char* name, uint8_t CrossPointSettings::* ptr, std::vector<std::string> values) {
-    return {name, SettingType::ENUM, ptr, std::move(values)};
+  static SettingInfo Enum(const char* name, uint8_t CrossPointSettings::* ptr, std::vector<std::string> values,
+                          const char* key = nullptr, const char* category = nullptr) {
+    SettingInfo s;
+    s.name = name;
+    s.type = SettingType::ENUM;
+    s.valuePtr = ptr;
+    s.enumValues = std::move(values);
+    s.key = key;
+    s.category = category;
+    return s;
   }
 
-  static SettingInfo Action(const char* name) { return {name, SettingType::ACTION, nullptr}; }
+  static SettingInfo Action(const char* name) {
+    SettingInfo s;
+    s.name = name;
+    s.type = SettingType::ACTION;
+    return s;
+  }
 
-  static SettingInfo Value(const char* name, uint8_t CrossPointSettings::* ptr, const ValueRange valueRange) {
-    return {name, SettingType::VALUE, ptr, {}, valueRange};
+  static SettingInfo Value(const char* name, uint8_t CrossPointSettings::* ptr, const ValueRange valueRange,
+                           const char* key = nullptr, const char* category = nullptr) {
+    SettingInfo s;
+    s.name = name;
+    s.type = SettingType::VALUE;
+    s.valuePtr = ptr;
+    s.valueRange = valueRange;
+    s.key = key;
+    s.category = category;
+    return s;
+  }
+
+  static SettingInfo String(const char* name, char* ptr, size_t maxLen, const char* key = nullptr,
+                            const char* category = nullptr) {
+    SettingInfo s;
+    s.name = name;
+    s.type = SettingType::STRING;
+    s.stringPtr = ptr;
+    s.stringMaxLen = maxLen;
+    s.key = key;
+    s.category = category;
+    return s;
+  }
+
+  static SettingInfo DynamicEnum(const char* name, std::vector<std::string> values, std::function<uint8_t()> getter,
+                                 std::function<void(uint8_t)> setter, const char* key = nullptr,
+                                 const char* category = nullptr) {
+    SettingInfo s;
+    s.name = name;
+    s.type = SettingType::ENUM;
+    s.enumValues = std::move(values);
+    s.valueGetter = std::move(getter);
+    s.valueSetter = std::move(setter);
+    s.key = key;
+    s.category = category;
+    return s;
+  }
+
+  static SettingInfo DynamicString(const char* name, std::function<std::string()> getter,
+                                   std::function<void(const std::string&)> setter, const char* key = nullptr,
+                                   const char* category = nullptr) {
+    SettingInfo s;
+    s.name = name;
+    s.type = SettingType::STRING;
+    s.stringGetter = std::move(getter);
+    s.stringSetter = std::move(setter);
+    s.key = key;
+    s.category = category;
+    return s;
   }
 };
 
@@ -48,7 +128,13 @@ class SettingsActivity final : public ActivityWithSubactivity {
   int selectedCategoryIndex = 0;  // Currently selected category
   int selectedSettingIndex = 0;
   int settingsCount = 0;
-  const SettingInfo* settingsList = nullptr;
+
+  // Per-category settings derived from shared list + device-only actions
+  std::vector<SettingInfo> displaySettings;
+  std::vector<SettingInfo> readerSettings;
+  std::vector<SettingInfo> controlsSettings;
+  std::vector<SettingInfo> systemSettings;
+  const std::vector<SettingInfo>* currentSettings = nullptr;
 
   const std::function<void()> onGoHome;