feat: add SD-backed stats archive and dedicated /stats web console

src/helpers/ArchiveStorage.h

@@ -0,0 +1,59 @@
+#pragma once
+
+#include <Arduino.h>
+#include <helpers/IdentityStore.h>
+
+#if defined(ESP32)
+  #include <FS.h>
+  #include <SD.h>
+  #include <SPI.h>
+#endif
+
+class ArchiveStorage {
+public:
+  ArchiveStorage();
+
+  void begin();
+  bool recover();
+
+  bool isSupported() const;
+  bool isAttempted() const { return _attempted; }
+  bool isMounted() const { return _mounted; }
+  bool hadMountFailure() const { return _mount_failed; }
+
+  const char* getLogicalName() const { return "archive"; }
+  const char* getLogicalStatsPath() const { return "archive:/stats"; }
+  const char* getFsStatsPath() const { return "/stats"; }
+
+  FILESYSTEM* getFS();
+
+  uint64_t getCardSizeBytes() const { return _card_size_bytes; }
+  uint64_t getTotalBytes() const { return _total_bytes; }
+  uint64_t getUsedBytes() const { return _used_bytes; }
+  const char* getCardTypeName() const;
+  uint8_t getChipSelectPin() const { return _cs_pin; }
+
+private:
+#if defined(ESP32)
+  bool resolvePins();
+  void refreshCardInfo();
+#endif
+
+  bool _attempted;
+  bool _mounted;
+  bool _mount_failed;
+  bool _supported;
+  uint8_t _card_type;
+  uint8_t _spi_bus;
+  uint8_t _cs_pin;
+  uint8_t _sck_pin;
+  uint8_t _miso_pin;
+  uint8_t _mosi_pin;
+  uint64_t _card_size_bytes;
+  uint64_t _total_bytes;
+  uint64_t _used_bytes;
+
+#if defined(ESP32)
+  SPIClass* _spi;
+#endif
+};