fix: use RAII render lock everywhere (#916)

## Summary

Follow-up to
https://github.com/crosspoint-reader/crosspoint-reader/pull/774

---

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Did you use AI tools to help write this code? **NO**


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

## Release Notes

* **Refactor**
* Modernized internal synchronization mechanisms across multiple
components to improve code reliability and maintainability. All
functionality remains unchanged.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

src/activities/settings/ClearCacheActivity.cpp

@@ -118,9 +118,10 @@ void ClearCacheActivity::loop() {
   if (state == WARNING) {
     if (mappedInput.wasPressed(MappedInputManager::Button::Confirm)) {
       LOG_DBG("CLEAR_CACHE", "User confirmed, starting cache clear");
-      xSemaphoreTake(renderingMutex, portMAX_DELAY);
-      state = CLEARING;
-      xSemaphoreGive(renderingMutex);
+      {
+        RenderLock lock(*this);
+        state = CLEARING;
+      }
       requestUpdateAndWait();
 
       clearCache();

src/activities/settings/KOReaderAuthActivity.cpp

@@ -14,18 +14,20 @@ void KOReaderAuthActivity::onWifiSelectionComplete(const bool success) {
   exitActivity();
 
   if (!success) {
-    xSemaphoreTake(renderingMutex, portMAX_DELAY);
-    state = FAILED;
-    errorMessage = "WiFi connection failed";
-    xSemaphoreGive(renderingMutex);
+    {
+      RenderLock lock(*this);
+      state = FAILED;
+      errorMessage = "WiFi connection failed";
+    }
     requestUpdate();
     return;
   }
 
-  xSemaphoreTake(renderingMutex, portMAX_DELAY);
-  state = AUTHENTICATING;
-  statusMessage = "Authenticating...";
-  xSemaphoreGive(renderingMutex);
+  {
+    RenderLock lock(*this);
+    state = AUTHENTICATING;
+    statusMessage = "Authenticating...";
+  }
   requestUpdate();
 
   performAuthentication();
@@ -34,15 +36,16 @@ void KOReaderAuthActivity::onWifiSelectionComplete(const bool success) {
 void KOReaderAuthActivity::performAuthentication() {
   const auto result = KOReaderSyncClient::authenticate();
 
-  xSemaphoreTake(renderingMutex, portMAX_DELAY);
-  if (result == KOReaderSyncClient::OK) {
-    state = SUCCESS;
-    statusMessage = "Successfully authenticated!";
-  } else {
-    state = FAILED;
-    errorMessage = KOReaderSyncClient::errorString(result);
+  {
+    RenderLock lock(*this);
+    if (result == KOReaderSyncClient::OK) {
+      state = SUCCESS;
+      statusMessage = "Successfully authenticated!";
+    } else {
+      state = FAILED;
+      errorMessage = KOReaderSyncClient::errorString(result);
+    }
   }
-  xSemaphoreGive(renderingMutex);
   requestUpdate();
 }
 

src/activities/settings/KOReaderSettingsActivity.cpp

@@ -121,7 +121,6 @@ void KOReaderSettingsActivity::handleSelection() {
     // Authenticate
     if (!KOREADER_STORE.hasCredentials()) {
       // Can't authenticate without credentials - just show message briefly
-      xSemaphoreGive(renderingMutex);
       return;
     }
     exitActivity();

src/activities/settings/OtaUpdateActivity.cpp

@@ -20,33 +20,37 @@ void OtaUpdateActivity::onWifiSelectionComplete(const bool success) {
 
   LOG_DBG("OTA", "WiFi connected, checking for update");
 
-  xSemaphoreTake(renderingMutex, portMAX_DELAY);
-  state = CHECKING_FOR_UPDATE;
-  xSemaphoreGive(renderingMutex);
+  {
+    RenderLock lock(*this);
+    state = CHECKING_FOR_UPDATE;
+  }
   requestUpdateAndWait();
 
   const auto res = updater.checkForUpdate();
   if (res != OtaUpdater::OK) {
     LOG_DBG("OTA", "Update check failed: %d", res);
-    xSemaphoreTake(renderingMutex, portMAX_DELAY);
-    state = FAILED;
-    xSemaphoreGive(renderingMutex);
+    {
+      RenderLock lock(*this);
+      state = FAILED;
+    }
     requestUpdate();
     return;
   }
 
   if (!updater.isUpdateNewer()) {
     LOG_DBG("OTA", "No new update available");
-    xSemaphoreTake(renderingMutex, portMAX_DELAY);
-    state = NO_UPDATE;
-    xSemaphoreGive(renderingMutex);
+    {
+      RenderLock lock(*this);
+      state = NO_UPDATE;
+    }
     requestUpdate();
     return;
   }
 
-  xSemaphoreTake(renderingMutex, portMAX_DELAY);
-  state = WAITING_CONFIRMATION;
-  xSemaphoreGive(renderingMutex);
+  {
+    RenderLock lock(*this);
+    state = WAITING_CONFIRMATION;
+  }
   requestUpdate();
 }