feat: unify navigation handling with system-wide continuous navigation (#600)

This PR unifies navigation handling & adds system-wide support for
continuous navigation.

## Summary
Holding down a navigation button now continuously advances through items
until the button is released. This removes the need for repeated
press-and-release actions and makes navigation faster and smoother,
especially in long menus or documents.

When page-based navigation is available, it will navigate through pages.
If not, it will progress through menu items or similar list-based UI
elements.

Additionally, this PR fixes inconsistencies in wrap-around behavior and
navigation index calculations.

Places where the navigation system was updated:
- Home Page
- Settings Pages
- My Library Page
- WiFi Selection Page
- OPDS Browser Page
- Keyboard
- File Transfer Page
- XTC Chapter Selector Page
- EPUB Chapter Selector Page

I’ve tested this on the device as much as possible and tried to match
the existing behavior. Please let me know if I missed anything. Thanks 🙏


![crosspoint](https://github.com/user-attachments/assets/6a3c7482-f45e-4a77-b156-721bb3b679e6)

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Following the request from @osteotek and @daveallie for system-wide
support, the old PR (#379) has been closed in favor of this
consolidated, system-wide implementation.

---

### AI Usage

Did you use AI tools to help write this code? _**PARTIALLY**_

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

src/activities/browser/OpdsBookBrowserActivity.h

@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "../ActivityWithSubactivity.h"
+#include "util/ButtonNavigator.h"
 
 /**
  * Activity for browsing and downloading books from an OPDS server.
@@ -37,6 +38,7 @@ class OpdsBookBrowserActivity final : public ActivityWithSubactivity {
  private:
   TaskHandle_t displayTaskHandle = nullptr;
   SemaphoreHandle_t renderingMutex = nullptr;
+  ButtonNavigator buttonNavigator;
   bool updateRequired = false;
 
   BrowserState state = BrowserState::LOADING;