LineageOS 18.1 (A11) for bach — 20260907 (modem fix)

Update over 20260618 — the modem works again, and USB tethering with it.

• SIM and mobile data are back. Since the move to Android 11 the modem was never
  initialised: rild resolves its RIL library from rild.libpath, a property this port
  stopped emitting, and unset it slept forever while init.svc.ril-daemon read running.
• USB tethering works again. The vendor's RNDIS composition depends on
  persist.vendor.usb.config.extra; unset, the USB gadget was never reconfigured.
• 42 further properties restored, all live on 17.1 and since dropped — RIL behaviour,
  the data path, display, audio, Bluetooth, the FRP block device. Each kept only after its
  reader was found in a shipped binary. Ledger in docs/LOST-PROPS.md.

Unchanged: SELinux enforcing, the CVE-backported kernel, cameras, audio, Wi-Fi/BT, sensors.