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/network/CalibreWirelessActivity.h

@@ -0,0 +1,135 @@
+#pragma once
+#include <SDCardManager.h>
+#include <WiFiClient.h>
+#include <WiFiUdp.h>
+#include <freertos/FreeRTOS.h>
+#include <freertos/semphr.h>
+#include <freertos/task.h>
+
+#include <functional>
+#include <string>
+
+#include "activities/Activity.h"
+
+/**
+ * CalibreWirelessActivity implements Calibre's "wireless device" protocol.
+ * This allows Calibre desktop to send books directly to the device over WiFi.
+ *
+ * Protocol specification sourced from Calibre's smart device driver:
+ * https://github.com/kovidgoyal/calibre/blob/master/src/calibre/devices/smart_device_app/driver.py
+ *
+ * Protocol overview:
+ * 1. Device broadcasts "hello" on UDP ports 54982, 48123, 39001, 44044, 59678
+ * 2. Calibre responds with its TCP server address
+ * 3. Device connects to Calibre's TCP server
+ * 4. Calibre sends JSON commands with length-prefixed messages
+ * 5. Books are transferred as binary data after SEND_BOOK command
+ */
+class CalibreWirelessActivity final : public Activity {
+  // Calibre wireless device states
+  enum class WirelessState {
+    DISCOVERING,   // Listening for Calibre server broadcasts
+    CONNECTING,    // Establishing TCP connection
+    WAITING,       // Connected, waiting for commands
+    RECEIVING,     // Receiving a book file
+    COMPLETE,      // Transfer complete
+    DISCONNECTED,  // Calibre disconnected
+    ERROR          // Connection/transfer error
+  };
+
+  // Calibre protocol opcodes (from calibre/devices/smart_device_app/driver.py)
+  enum OpCode : uint8_t {
+    OK = 0,
+    SET_CALIBRE_DEVICE_INFO = 1,
+    SET_CALIBRE_DEVICE_NAME = 2,
+    GET_DEVICE_INFORMATION = 3,
+    TOTAL_SPACE = 4,
+    FREE_SPACE = 5,
+    GET_BOOK_COUNT = 6,
+    SEND_BOOKLISTS = 7,
+    SEND_BOOK = 8,
+    GET_INITIALIZATION_INFO = 9,
+    BOOK_DONE = 11,
+    NOOP = 12,  // Was incorrectly 18
+    DELETE_BOOK = 13,
+    GET_BOOK_FILE_SEGMENT = 14,
+    GET_BOOK_METADATA = 15,
+    SEND_BOOK_METADATA = 16,
+    DISPLAY_MESSAGE = 17,
+    CALIBRE_BUSY = 18,
+    SET_LIBRARY_INFO = 19,
+    ERROR = 20,
+  };
+
+  TaskHandle_t displayTaskHandle = nullptr;
+  TaskHandle_t networkTaskHandle = nullptr;
+  SemaphoreHandle_t renderingMutex = nullptr;
+  SemaphoreHandle_t stateMutex = nullptr;
+  bool updateRequired = false;
+
+  WirelessState state = WirelessState::DISCOVERING;
+  const std::function<void()> onComplete;
+
+  // UDP discovery
+  WiFiUDP udp;
+
+  // TCP connection (we connect to Calibre)
+  WiFiClient tcpClient;
+  std::string calibreHost;
+  uint16_t calibrePort = 0;
+  uint16_t calibreAltPort = 0;  // Alternative port (content server)
+  std::string calibreHostname;
+
+  // Transfer state
+  std::string currentFilename;
+  size_t currentFileSize = 0;
+  size_t bytesReceived = 0;
+  std::string statusMessage;
+  std::string errorMessage;
+
+  // Protocol state
+  bool inBinaryMode = false;
+  size_t binaryBytesRemaining = 0;
+  FsFile currentFile;
+  std::string recvBuffer;  // Buffer for incoming data (like KOReader)
+
+  static void displayTaskTrampoline(void* param);
+  static void networkTaskTrampoline(void* param);
+  [[noreturn]] void displayTaskLoop();
+  [[noreturn]] void networkTaskLoop();
+  void render() const;
+
+  // Network operations
+  void listenForDiscovery();
+  void handleTcpClient();
+  bool readJsonMessage(std::string& message);
+  void sendJsonResponse(OpCode opcode, const std::string& data);
+  void handleCommand(OpCode opcode, const std::string& data);
+  void receiveBinaryData();
+
+  // Protocol handlers
+  void handleGetInitializationInfo(const std::string& data);
+  void handleGetDeviceInformation();
+  void handleFreeSpace();
+  void handleGetBookCount();
+  void handleSendBook(const std::string& data);
+  void handleSendBookMetadata(const std::string& data);
+  void handleDisplayMessage(const std::string& data);
+  void handleNoop(const std::string& data);
+
+  // Utility
+  std::string getDeviceUuid() const;
+  void setState(WirelessState newState);
+  void setStatus(const std::string& message);
+  void setError(const std::string& message);
+
+ public:
+  explicit CalibreWirelessActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
+                                   const std::function<void()>& onComplete)
+      : Activity("CalibreWireless", renderer, mappedInput), onComplete(onComplete) {}
+  void onEnter() override;
+  void onExit() override;
+  void loop() override;
+  bool preventAutoSleep() override { return true; }
+  bool skipLoopDelay() override { return true; }
+};