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.

Start by locating the dApp-browser plugin to remove the native-navbar API and events. Then find the iOS overlay window and Android navbar manager, views, and related resources. Verify that React BottomNav remains the only navigation by building the packages and running targeted tests. Ensure embedded dApp WebView behavior is unchanged after removal.

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