fix: chore: make all debug messages uniform (#825)

## Summary

* Unify all serial port debug messages

## Additional Context

* All messages sent to the serial port now follow the "[timestamp]
[origin] payload" format (notable exception framework messages)

---

### AI Usage

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please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? No

src/activities/home/RecentBooksActivity.cpp

@@ -73,7 +73,7 @@ void RecentBooksActivity::loop() {
 
   if (mappedInput.wasReleased(MappedInputManager::Button::Confirm)) {
     if (!recentBooks.empty() && selectorIndex < static_cast<int>(recentBooks.size())) {
-      Serial.printf("Selected recent book: %s\n", recentBooks[selectorIndex].path.c_str());
+      Serial.printf("[%lu] [RBA] Selected recent book: %s\n", millis(), recentBooks[selectorIndex].path.c_str());
       onSelectBook(recentBooks[selectorIndex].path);
       return;
     }