Adds margin setting and calibre web

Also made the menu items dynamic and capital case. Looks better from a design perspective but I suppose this is an optional thing to accept

src/activities/browser/OpdsBookBrowserActivity.h

@@ -0,0 +1,56 @@
+#pragma once
+#include <OpdsParser.h>
+#include <freertos/FreeRTOS.h>
+#include <freertos/semphr.h>
+#include <freertos/task.h>
+
+#include <functional>
+#include <string>
+#include <vector>
+
+#include "../Activity.h"
+
+/**
+ * Activity for browsing and downloading books from an OPDS server.
+ * Displays a list of available books and allows downloading EPUBs.
+ */
+class OpdsBookBrowserActivity final : public Activity {
+ public:
+  enum class BrowserState {
+    LOADING,      // Fetching OPDS feed
+    BOOK_LIST,    // Displaying books
+    DOWNLOADING,  // Downloading selected EPUB
+    ERROR         // Error state with message
+  };
+
+  explicit OpdsBookBrowserActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
+                                   const std::function<void()>& onGoHome)
+      : Activity("OpdsBookBrowser", renderer, mappedInput), onGoHome(onGoHome) {}
+
+  void onEnter() override;
+  void onExit() override;
+  void loop() override;
+
+ private:
+  TaskHandle_t displayTaskHandle = nullptr;
+  SemaphoreHandle_t renderingMutex = nullptr;
+  bool updateRequired = false;
+
+  BrowserState state = BrowserState::LOADING;
+  std::vector<OpdsBook> books;
+  int selectorIndex = 0;
+  std::string errorMessage;
+  std::string statusMessage;
+  size_t downloadProgress = 0;
+  size_t downloadTotal = 0;
+
+  const std::function<void()> onGoHome;
+
+  static void taskTrampoline(void* param);
+  [[noreturn]] void displayTaskLoop();
+  void render() const;
+
+  void fetchBooks();
+  void downloadBook(const OpdsBook& book);
+  std::string sanitizeFilename(const std::string& title) const;
+};