Remove the retired native navbar bridge and platform overlays

## Problem

Commit `5fd95811` retired the JavaScript side of the native mobile navbar and moved the persistent wallet navigation to React `BottomNav`. The Swift and Android overlay implementations, plugin methods, events, resources, and dApp-dialog integration remain compiled in the repository, but no live wallet source calls them.

Keeping this unreachable implementation creates maintenance work and makes the current architecture difficult to determine. PR #807 exposed this by fixing an Android four-item layout bug in code that cannot currently render.

## Scope

- Remove the native-navbar plugin API and event surface from the bundled dApp-browser package.
- Remove the iOS overlay window and navbar-specific controls.
- Remove the Android navbar manager, views, state classes, drawables, colors, and dialog/activity integration.
- Remove generated declarations or documentation that expose the retired API.
- Keep the native dApp WebView behavior unchanged.

## Acceptance criteria

- [ ] No callable native-navbar methods or events remain in the dApp-browser plugin.
- [ ] No native navbar view is compiled into the iOS or Android app.
- [ ] Opening, switching, and closing embedded dApps continues to work.
- [ ] React `BottomNav` remains the only persistent wallet navigation implementation.
- [ ] Relevant package builds, wallet type checks, and targeted tests pass.
- [ ] `git diff --check` passes.

Found while validating #802 in PR #807.