[combobox] Disabled Trigger omits native disabled during SSR and causes a hydration mismatch

# Bug report

## Current behavior

A disabled `Combobox.Trigger` produces different native button attributes during SSR and hydration.

The component receives `disabled={true}` during both SSR and the first client render. However, the server HTML contains:

```html
Open
```

while the first client render expects:

```html
Open
```

React reports:

```diff

```

The full warning is:

```text
A tree hydrated but some attributes of the server rendered HTML
didn't match the client properties. This won't be patched up.
```

## Expected behavior

When `disabled={true}`, `Combobox.Trigger` should produce the same native `disabled` attribute during SSR and the first client render.

Hydrating the component should not produce a warning.

## Reproducible example

This is the minimal component that reproduces the problem in my TanStack Start SSR application:

```tsx
import { Combobox } from "@base-ui/react/combobox";

export function Example() {
return (

Open

);
}
```

I do not currently have a hosted reproduction, but I can create one if the issue cannot be reproduced from this example.

## Base UI version

v1.8.0

## Which browser are you using?

Chrome

## Which OS are you using?

Linux

## Which assistive tech are you using (if applicable)?

This was created with the help of Microsoft Copilot (GPT 5.6 Think deeper)

## Additional context

Relevant versions:

```text
react: 19.2.5
react-dom: 19.2.5
@base-ui/react: 1.8.0
@tanstack/react-start: 1.168.25
```

I confirmed that the logical state is the same during SSR and the first client render:

```text
SSR:
disabled = true

First client render:
disabled = true
```

I also tested the following:

- Passing `disabled` directly to `Combobox.Root`
- Passing `disabled` to both `Combobox.Root` and `Combobox.Trigger`
- Removing the custom `render` prop
- Rendering the native Base UI trigger directly
- Removing all items, values, controlled state, and API-query logic

The same mismatch still occurs with the minimal Combobox.

The Base UI state attribute `data-disabled=""` is present in both cases. Only the native `disabled` attribute differs.

Could this be an SSR issue in `Combobox.Trigger` or Base UI's internal native-button handling?

Start with the minimal SSR example using Combobox.Root and Combobox.Trigger, then inspect the Combobox.Trigger native-button handling described in the report. Reproduce the server and first client renders with disabled={true}; done means both contain the native disabled attribute and hydration produces no warning.

Written by the indexing model from the issue text.