Calibre Web Epub Downloading + Calibre Wireless Device Syncing (#219)

## Summary

Adds support for browsing and downloading books from a Calibre-web
server via OPDS.
How it works
1. Configure server URL in Settings → Calibre Web URL (e.g.,
https://myserver.com:port I use Cloudflare tunnel to make my server
accessible anywhere fwiw)
2. "Calibre Library" will now show on the the home screen
3. Browse the catalog - navigate through categories like "By Newest",
"By Author", "By Series", etc.
4. Download books - select a book and press Confirm to download the EPUB
to your device
Navigation
- Up/Down - Move through entries
- Confirm - Open folder or download book
- Back - Go to parent catalog, or exit to home if at root
- Navigation entries show with > prefix, books show title and author
- Button hints update dynamically ("Open" for folders, "Download" for
books)
Technical details
- Fetches OPDS catalog from {server_url}/opds
- Parses both navigation feeds (catalog links) and acquisition feeds
(downloadable books)
- Maintains navigation history stack for back navigation
- Handles absolute paths in OPDS links correctly (e.g.,
/books/opds/navcatalog/...)
- Downloads EPUBs directly to the SD card root
Note
The server URL should be typed to include https:// if the server
requires it - HTTP→HTTPS redirects may cause SSL errors on ESP32.

## Additional Context

* I also changed the home titles to use uppercase for each word and
added a setting to change the size of the side margins

---------

Co-authored-by: Dave Allie <dave@daveallie.com>

src/activities/browser/OpdsBookBrowserActivity.h

@@ -0,0 +1,61 @@
+#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.
+ * Supports navigation through catalog hierarchy and downloading EPUBs.
+ */
+class OpdsBookBrowserActivity final : public Activity {
+ public:
+  enum class BrowserState {
+    CHECK_WIFI,   // Checking WiFi connection
+    LOADING,      // Fetching OPDS feed
+    BROWSING,     // Displaying entries (navigation or 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<OpdsEntry> entries;
+  std::vector<std::string> navigationHistory;  // Stack of previous feed paths for back navigation
+  std::string currentPath;                     // Current feed path being displayed
+  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 checkAndConnectWifi();
+  void fetchFeed(const std::string& path);
+  void navigateToEntry(const OpdsEntry& entry);
+  void navigateBack();
+  void downloadBook(const OpdsEntry& book);
+};