refactor: Eliminated relative path includes (#1961)

## Summary

Relative includes can hide inappropriate dependency relationships. In
this case, I found that lib/KOReaderSync/KOReaderCredentialStore.cpp was
dependent on src/JsonSettingsIO.h -- a lib -> app dependency, the
opposite direction dependencies should flow in this project.

This change replaces all relative includes with root-relative includes,
and corrects the KOReaderCredentialStore dependency by moving its JSON
settings serialization local to the KOReaderSync library.

---

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lib/KOReaderSync/KOReaderCredentialStore.cpp

@@ -6,7 +6,7 @@
 #include <ObfuscationUtils.h>
 #include <Serialization.h>
 
-#include "../../src/JsonSettingsIO.h"
+#include "KOReaderJsonIO.h"
 
 // Initialize the static instance
 KOReaderCredentialStore KOReaderCredentialStore::instance;
@@ -36,7 +36,7 @@ void legacyDeobfuscate(std::string& data) {
 
 bool KOReaderCredentialStore::saveToFile() const {
   Storage.mkdir("/.crosspoint");
-  return JsonSettingsIO::saveKOReader(*this, KOREADER_FILE_JSON);
+  return KOReaderJsonIO::save(*this, KOREADER_FILE_JSON);
 }
 
 bool KOReaderCredentialStore::loadFromFile() {
@@ -45,7 +45,7 @@ bool KOReaderCredentialStore::loadFromFile() {
     String json = Storage.readFile(KOREADER_FILE_JSON);
     if (!json.isEmpty()) {
       bool resave = false;
-      bool result = JsonSettingsIO::loadKOReader(*this, json.c_str(), &resave);
+      bool result = KOReaderJsonIO::load(*this, json.c_str(), &resave);
       if (result && resave) {
         saveToFile();
         LOG_DBG("KRS", "Resaved KOReader credentials to update format");

lib/KOReaderSync/KOReaderCredentialStore.h

@@ -8,12 +8,6 @@ enum class DocumentMatchMethod : uint8_t {
   BINARY = 1,    // Match by partial MD5 of file content (more accurate, but files must be identical)
 };
 
-class KOReaderCredentialStore;
-namespace JsonSettingsIO {
-bool saveKOReader(const KOReaderCredentialStore& store, const char* path);
-bool loadKOReader(KOReaderCredentialStore& store, const char* json, bool* needsResave);
-}  // namespace JsonSettingsIO
-
 /**
  * Singleton class for storing KOReader sync credentials on the SD card.
  * Passwords are XOR-obfuscated with the device's unique hardware MAC address
@@ -33,9 +27,6 @@ class KOReaderCredentialStore {
 
   bool loadFromBinaryFile();
 
-  friend bool JsonSettingsIO::saveKOReader(const KOReaderCredentialStore&, const char*);
-  friend bool JsonSettingsIO::loadKOReader(KOReaderCredentialStore&, const char*, bool*);
-
  public:
   // Delete copy constructor and assignment
   KOReaderCredentialStore(const KOReaderCredentialStore&) = delete;

lib/KOReaderSync/KOReaderJsonIO.cpp

@@ -0,0 +1,51 @@
+#include "KOReaderJsonIO.h"
+
+#include <ArduinoJson.h>
+#include <HalStorage.h>
+#include <Logging.h>
+#include <ObfuscationUtils.h>
+
+#include "KOReaderCredentialStore.h"
+
+namespace KOReaderJsonIO {
+
+bool save(const KOReaderCredentialStore& store, const char* path) {
+  JsonDocument doc;
+  doc["username"] = store.getUsername();
+  doc["password_obf"] = obfuscation::obfuscateToBase64(store.getPassword());
+  doc["serverUrl"] = store.getServerUrl();
+  doc["matchMethod"] = static_cast<uint8_t>(store.getMatchMethod());
+
+  String json;
+  serializeJson(doc, json);
+  return Storage.writeFile(path, json);
+}
+
+bool load(KOReaderCredentialStore& store, const char* json, bool* needsResave) {
+  if (needsResave) *needsResave = false;
+  JsonDocument doc;
+  auto error = deserializeJson(doc, json);
+  if (error) {
+    LOG_ERR("KRS", "JSON parse error: %s", error.c_str());
+    return false;
+  }
+
+  std::string user = doc["username"] | std::string("");
+
+  bool ok = false;
+  std::string pass = obfuscation::deobfuscateFromBase64(doc["password_obf"] | "", &ok);
+  if (!ok || pass.empty()) {
+    pass = doc["password"] | std::string("");
+    if (!pass.empty() && needsResave) *needsResave = true;
+  }
+
+  store.setCredentials(user, pass);
+  store.setServerUrl(doc["serverUrl"] | std::string(""));
+
+  uint8_t method = doc["matchMethod"] | (uint8_t)0;
+  store.setMatchMethod(static_cast<DocumentMatchMethod>(method));
+
+  return true;
+}
+
+}  // namespace KOReaderJsonIO

lib/KOReaderSync/KOReaderJsonIO.h

@@ -0,0 +1,8 @@
+#pragma once
+
+class KOReaderCredentialStore;
+
+namespace KOReaderJsonIO {
+bool save(const KOReaderCredentialStore& store, const char* path);
+bool load(KOReaderCredentialStore& store, const char* json, bool* needsResave);
+}  // namespace KOReaderJsonIO