refactor: rename MyLibrary to FileBrowser (#1260)

## Summary

* Renames MyLibrary component to FileBrowser, as it better reflects what
it is, in my opinion

## Additional Context

* Frees the Library name for possible future library component that can
cache metadata, provide other ways of browsing than filesystem
structure, etc
---

### AI Usage

Did you use AI tools to help write this code? _**< YES >**_

src/activities/home/HomeActivity.cpp

@@ -20,7 +20,7 @@
 #include "util/StringUtils.h"
 
 int HomeActivity::getMenuItemCount() const {
-  int count = 4;  // My Library, Recents, File transfer, Settings
+  int count = 4;  // File Browser, Recents, File transfer, Settings
   if (!recentBooks.empty()) {
     count += recentBooks.size();
   }
@@ -189,7 +189,7 @@ void HomeActivity::loop() {
     // Calculate dynamic indices based on which options are available
     int idx = 0;
     int menuSelectedIndex = selectorIndex - static_cast<int>(recentBooks.size());
-    const int myLibraryIdx = idx++;
+    const int fileBrowserIdx = idx++;
     const int recentsIdx = idx++;
     const int opdsLibraryIdx = hasOpdsUrl ? idx++ : -1;
     const int fileTransferIdx = idx++;
@@ -197,8 +197,8 @@ void HomeActivity::loop() {
 
     if (selectorIndex < recentBooks.size()) {
       onSelectBook(recentBooks[selectorIndex].path);
-    } else if (menuSelectedIndex == myLibraryIdx) {
-      onMyLibraryOpen();
+    } else if (menuSelectedIndex == fileBrowserIdx) {
+      onFileBrowserOpen();
     } else if (menuSelectedIndex == recentsIdx) {
       onRecentsOpen();
     } else if (menuSelectedIndex == opdsLibraryIdx) {
@@ -231,7 +231,7 @@ void HomeActivity::render(RenderLock&&) {
   std::vector<UIIcon> menuIcons = {Folder, Recent, Transfer, Settings};
 
   if (hasOpdsUrl) {
-    // Insert OPDS Browser after My Library
+    // Insert OPDS Browser after File Browser
     menuItems.insert(menuItems.begin() + 2, tr(STR_OPDS_BROWSER));
     menuIcons.insert(menuIcons.begin() + 2, Library);
   }
@@ -261,7 +261,7 @@ void HomeActivity::render(RenderLock&&) {
 
 void HomeActivity::onSelectBook(const std::string& path) { activityManager.goToReader(path); }
 
-void HomeActivity::onMyLibraryOpen() { activityManager.goToMyLibrary(); }
+void HomeActivity::onFileBrowserOpen() { activityManager.goToFileBrowser(); }
 
 void HomeActivity::onRecentsOpen() { activityManager.goToRecentBooks(); }