Remove Bluetooth from multiplayer

Multiplayer now runs over Wi-Fi (LAN) only.

- Delete BluetoothTransport and drop it from LobbyController's transport
  list, leaving LanTransport as the sole transport.
- Drop TransportKind.BLUETOOTH and the now-unused RFCOMM_UUID constant.
- Remove the BLUETOOTH/BLUETOOTH_ADMIN/BLUETOOTH_CONNECT permissions and
  the android.hardware.bluetooth feature from the manifest, along with
  the runtime permission request in MainActivity and the
  requestBluetoothPermissions hook on AppEnv.
- Update lobby copy so an empty transport list and an empty host list
  talk about Wi-Fi rather than pairing, and refresh the comments and
  README sections that described two transports.

The transport abstraction itself is kept: everything after the handshake
was already transport independent, so adding another one later needs no
changes above LanTransport.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01YEsqYAMJKUJoM7UAavm169

app/src/test/java/org/prolibertate/games/net/SeatForDeviceTest.kt

@@ -33,10 +33,10 @@ class SeatForDeviceTest {
      * The regression this exists for.
      *
      * The seat used to be looked up by [PlayerSlot.peerId], which is the address
-     * the host's own transport made up for the incoming link — an IP on Wi-Fi, a
-     * MAC over Bluetooth. A guest has never seen that value and so never matched
-     * it, and every guest fell through to "the first seat held by somebody
-     * remote". With one guest that is right by luck. With two, both of them
+     * the host's own transport made up for the incoming link — an IP on Wi-Fi. A
+     * guest has never seen that value and so never matched it, and every guest
+     * fell through to "the first seat held by somebody remote". With one guest
+     * that is right by luck. With two, both of them
      * claimed seat 1, and the one really sitting in seat 2 was left looking at a
      * table with no cards in front of it.
      */