fix(android): declare background location permission

[Zarah636]

What changed

Added android.permission.ACCESS_BACKGROUND_LOCATION to the Android manifest of the wifi_ssid plugin.

Why

FlClash's on-demand mode reads the current Wi-Fi SSID to decide whether the proxy should run. On Android 10 and later, users cannot grant “Allow all the time” location access unless the app explicitly declares ACCESS_BACKGROUND_LOCATION.

Without that declaration, SSID reads may return null after FlClash moves to the background, so Wi-Fi-based on-demand rules do not run reliably.

Scope

This is a manifest-only change. It does not modify VPN lifecycle handling, background services, or code for other platforms. The permission is used to allow background Wi-Fi SSID access; this change does not add location-coordinate collection.

Users still need to grant “Allow all the time” location access in Android system settings. Device-specific battery restrictions or process termination may still affect background execution.

Verification

• Confirmed the PR diff contains one added line in one file.
• Parsed the modified Android manifest successfully.
• git diff --check passes.
• Built an Android ARM64 release APK from the same upstream commit with this manifest change.
• Verified with aapt2 that both ACCESS_FINE_LOCATION and ACCESS_BACKGROUND_LOCATION are present in the resulting APK.

Fixes #2233