chore: Refactor stores to use PersistableStore CRTP template (#2464)

lib/Serialization/PersistableStore.cpp

@@ -0,0 +1,45 @@
+#include "PersistableStore.h"
+
+#include <HalStorage.h>
+#include <Logging.h>
+#include <ObfuscationUtils.h>
+
+bool PersistableStoreBase::writeDocToFile(const char* path, const JsonDocument& doc) {
+  Storage.mkdir("/.crosspoint");
+  String json;
+  serializeJson(doc, json);
+  if (!Storage.writeFile(path, json)) {
+    LOG_ERR("PERSIST", "Failed to write %s", path);
+    return false;
+  }
+  return true;
+}
+
+bool PersistableStoreBase::readDocFromFile(const char* path, JsonDocument& doc) {
+  if (!Storage.exists(path)) {
+    return false;  // Expected on first boot — not an error.
+  }
+  String json = Storage.readFile(path);
+  if (json.isEmpty()) {
+    LOG_ERR("PERSIST", "Failed to read %s (empty)", path);
+    return false;
+  }
+  auto error = deserializeJson(doc, json);
+  if (error) {
+    LOG_ERR("PERSIST", "JSON parse error in %s: %s", path, error.c_str());
+    return false;
+  }
+  return true;
+}
+
+std::string PersistableStoreBase::extractPassword(JsonVariantConst doc, bool& needsResave) {
+  bool ok = false;
+  std::string pass = obfuscation::deobfuscateFromBase64(doc["password_obf"] | "", &ok);
+  if (!ok) {
+    // Deobfuscation failed — fall back to legacy plaintext password.
+    pass = doc["password"] | "";
+    if (!pass.empty()) needsResave = true;
+  }
+  // A successfully decoded empty string is a legitimate value; preserve as-is.
+  return pass;
+}