feat: A web editor for settings (#667)

## Summary

This is an updated version of @itsthisjustin's #346 that builds on
current master and also deduplicates the settings list so we don't have
two copies of the settings. In the Web UI, it should organize the
settings a little closer to what you see on device.

## Additional Context

I tested this live on device and it seems to play nicely for me. It's
re-based on master since master's settings stuff has moved somewhat
since the original PR and addresses the sole review comment #346 - it
also means that I don't need to manually key in the URL for my OPDS
server. :)

---

### AI Usage

My changes were implemented with Claude Opus 4.5 and Claude Code 2.1.25.
I don't know if @itsthisjustin's original work used AI assistance.

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

src/network/CrossPointWebServer.h

@@ -100,4 +100,9 @@ class CrossPointWebServer {
   void handleRename() const;
   void handleMove() const;
   void handleDelete() const;
+
+  // Settings handlers
+  void handleSettingsPage() const;
+  void handleGetSettings() const;
+  void handlePostSettings();
 };