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/CrossPointSettings.cpp

@@ -4,6 +4,8 @@
 #include <SDCardManager.h>
 #include <Serialization.h>
 
+#include <cstring>
+
 #include "fontIds.h"
 
 // Initialize the static instance
@@ -12,7 +14,7 @@ CrossPointSettings CrossPointSettings::instance;
 namespace {
 constexpr uint8_t SETTINGS_FILE_VERSION = 1;
 // Increment this when adding new persisted settings fields
-constexpr uint8_t SETTINGS_COUNT = 15;
+constexpr uint8_t SETTINGS_COUNT = 16;
 constexpr char SETTINGS_FILE[] = "/.crosspoint/settings.bin";
 }  // namespace
 
@@ -40,6 +42,7 @@ bool CrossPointSettings::saveToFile() const {
   serialization::writePod(outputFile, paragraphAlignment);
   serialization::writePod(outputFile, sleepTimeout);
   serialization::writePod(outputFile, refreshFrequency);
+  serialization::writeString(outputFile, std::string(opdsServerUrl));
   serialization::writePod(outputFile, screenMargin);
   serialization::writePod(outputFile, sleepScreenCoverMode);
   outputFile.close();
@@ -94,10 +97,16 @@ bool CrossPointSettings::loadFromFile() {
     if (++settingsRead >= fileSettingsCount) break;
     serialization::readPod(inputFile, refreshFrequency);
     if (++settingsRead >= fileSettingsCount) break;
+    {
+      std::string urlStr;
+      serialization::readString(inputFile, urlStr);
+      strncpy(opdsServerUrl, urlStr.c_str(), sizeof(opdsServerUrl) - 1);
+      opdsServerUrl[sizeof(opdsServerUrl) - 1] = '\0';
+    }
+    if (++settingsRead >= fileSettingsCount) break;
     serialization::readPod(inputFile, screenMargin);
     if (++settingsRead >= fileSettingsCount) break;
     serialization::readPod(inputFile, sleepScreenCoverMode);
-    if (++settingsRead >= fileSettingsCount) break;
   } while (false);
 
   inputFile.close();