feat: settings manager with NVS persistence

Co-authored-by: Cursor <cursoragent@cursor.com>

src/settings.h

@@ -0,0 +1,71 @@
+#pragma once
+
+#include <Arduino.h>
+#include "config.h"
+
+enum class CycleMode : uint8_t {
+    Random = 0,
+    Chronological = 1,
+    ReverseChronological = 2,
+    FavoritesWeighted = 3
+};
+
+enum class ImageQuality : uint8_t {
+    Preview = 0,
+    Original = 1
+};
+
+enum class MetaPosition : uint8_t {
+    Bottom = 0,
+    Top = 1
+};
+
+// Metadata flags bitmask
+constexpr uint8_t META_DATE     = 0x01;
+constexpr uint8_t META_LOCATION = 0x02;
+constexpr uint8_t META_PEOPLE   = 0x04;
+constexpr uint8_t META_ALBUM    = 0x08;
+constexpr uint8_t META_CAMERA   = 0x10;
+
+struct Settings {
+    // WiFi
+    String wifi_ssid;
+    String wifi_pass;
+
+    // Immich
+    String immich_url;
+    String immich_key;
+
+    // Slideshow
+    uint8_t interval_min;
+    CycleMode cycle_mode;
+    ImageQuality img_quality;
+
+    // Display
+    uint8_t meta_flags;
+    MetaPosition meta_pos;
+
+    // Device
+    uint8_t led_brightness;
+    uint32_t queue_cursor;
+    String albums_json;
+};
+
+class SettingsManager {
+public:
+    void begin();
+    Settings get();
+    void save(const Settings& s);
+    void saveField(const char* key, uint8_t value);
+    void saveField(const char* key, const char* value);
+    void factoryReset();
+    bool isProvisioned();
+
+private:
+    String readString(const char* key, const char* defaultValue = "");
+    uint8_t readU8(const char* key, uint8_t defaultValue = 0);
+    uint32_t readU32(const char* key, uint32_t defaultValue = 0);
+    void writeString(const char* key, const String& value);
+    void writeU8(const char* key, uint8_t value);
+    void writeU32(const char* key, uint32_t value);
+};