Expose BaseDocumentHandle in Root Context for Dioxus Native applications

## Problem Description

In `dioxus-native`, the runtime already exposes several key platform capabilities to the VirtualDom root scope (`ScopeId::ROOT`) during window initialization in `dioxus_application.rs`:

- `winit_window: Arc`
- `renderer: Renderer`
- `shell_provider: Arc`
- `history_provider: Rc`
- `document: Rc` (for page title and `` tags)

However, the underlying authority for native DOM operations — **`BaseDocument`** (which manages the node tree, layout geometry, Stylo styling, focus, and scrolling) — is currently inaccessible to components inside the `VirtualDom`.

Components and ecosystem UI libraries that need to perform DOM-level operations on Native (such as measuring bounding client rects for tooltips/popovers/selects, controlling node focus, or querying scroll offsets) currently have no standardized way to obtain a reference to the active native DOM authority without constructing custom window wrappers, engine forks, or ad-hoc workarounds.

## The Web vs. Native Ambient Acquisition Gap

When authoring cross-platform DOM abstractions and UI primitives:

- **On Web (`wasm32`)**: components and hooks can access the ambient document via `web_sys::window()?.document()`.
- **On Blitz Native**: the equivalent authority (`BaseDocument`) is owned by `DioxusDocument.inner`, but it is not exposed to the component tree.

This creates an asymmetry where native libraries must introduce extra platform-specific setup even when the underlying runtime already owns the needed document object.

## Proposed Solution: `BaseDocumentHandle`

Rather than exposing raw `Rc>` directly in Dioxus's type-based context system, introduce a neutral wrapper/newtype such as:

```rust
// packages/dioxus-native/src/contexts.rs
use blitz_dom::BaseDocument;
use std::cell::RefCell;
use std::rc::Rc;

#[derive(Clone)]
pub struct BaseDocumentHandle(Rc>);

impl BaseDocumentHandle {
pub fn new(inner: Rc>) -> Self {
Self(inner)
}

// Exact accessor surface intentionally left open to maintainer preference.
}
```

Then inject it into `ScopeId::ROOT` during native window creation:

```rust
let base_document_handle = BaseDocumentHandle::new(doc.inner.clone());
doc.vdom
.in_scope(ScopeId::ROOT, move || provide_context(base_document_handle));
```

thanks for reading

Start with packages/dioxus-native/src/contexts.rs and the native window initialization in dioxus_application.rs. Trace how DioxusDocument.inner is owned and how existing values enter ScopeId::ROOT, then verify that a BaseDocumentHandle is available to native components without exposing the raw document directly.

Written by the indexing model from the issue text.