App 2.4.0: pair with the server by QR code

The Server tab gets "Pair with phone" right under the server URL, which
is now pre-filled with https://car.stinnesbeck.com. It opens a dialog
with a QR code and the short code, polls the server, and on approval
saves this car's own token like Save would — nothing to type in the
car. Denied, expired, and pairing switched off on the server are each
reported. PairingClient is tested against a stand-in for the server.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QLJfZQZeAKAwSqViTmLzki

app/src/main/res/layout/pane_server.xml

@@ -6,6 +6,8 @@
             <com.google.android.material.textfield.TextInputLayout android:id="@+id/server_url_layout" style="@style/Widget.EV.Input" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="18dp" android:hint="@string/hint_server_url" app:helperText="@string/helper_server_url">
                 <com.google.android.material.textfield.TextInputEditText android:id="@+id/server_url_input" android:layout_width="match_parent" android:layout_height="wrap_content" android:minHeight="72dp" android:inputType="textUri" android:singleLine="true" android:textSize="20sp" />
             </com.google.android.material.textfield.TextInputLayout>
+            <com.google.android.material.button.MaterialButton android:id="@+id/server_pair_button" style="@style/Widget.EV.Button" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="16dp" android:text="@string/btn_pair" />
+            <TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="8dp" android:text="@string/pair_hint" android:textAppearance="@style/Text.EV.Secondary" />
             <com.google.android.material.textfield.TextInputLayout android:id="@+id/server_token_layout" style="@style/Widget.EV.Input" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="18dp" android:hint="@string/hint_server_token" app:endIconMode="password_toggle" app:endIconMinSize="72dp" app:helperText="@string/helper_server_token">
                 <com.google.android.material.textfield.TextInputEditText android:id="@+id/server_token_input" android:layout_width="match_parent" android:layout_height="wrap_content" android:minHeight="72dp" android:inputType="textPassword" android:singleLine="true" android:textSize="20sp" />
             </com.google.android.material.textfield.TextInputLayout>