Android Companion App WebView overrides download filename

**Home Assistant Android app version(s):**
Version 2026.2.1-full
**Android version(s):**
13 and 15 (phone /tablet)
**Device model(s):**
Galaxy Tab S7/other devices with android too
**Home Assistant version:**
2026.2.1
**Last working Home Assistant release (if known):**

**Description of problem, include YAML if issue is related to notifications:**
In the Home Assistant Companion App (Android), WebView downloads ignore the filename set via `.`
In a normal browser the filename is correct (e.g. `theme..css` or `prefs..json`).
In the Companion App it always saves as `Home Assistant YYYY-MM-DD HH-MM-SS.css/json`.

Steps to reproduce:
1. Open a custom HTML page in a HA WebView (panel/iframe).
2. Trigger a download using `` (also tested with `data:` URLs).
3. Save the file in the Companion App.

**Additional information:**