[feat](client): address one instance origin instead of connection modes

Apps reach every service through Maestro on one port; direct service addressing is no longer a supported deployment, and Maestro has no per-service hostname or host-port route. Replace the maestro/direct modes and the serviceRef lookup with one configured origin and the fixed paths /api/alarm/{action,auth,ws}, defaulting dev builds to 127.0.0.1:8080 through adb reverse. The old mode-specific body wrapping and the direct-mode socket branch go with it.

src/screens/LoginScreen.tsx

@@ -2,6 +2,7 @@ import React, { useState } from 'react';
 import { KeyboardAvoidingView, Platform, View } from 'react-native';
 import { useAuth } from '../state/AuthContext';
 import { useConnection } from '../state/ConnectionContext';
+import { navigationRef } from '../navigationRef';
 import {
   AppText,
   Button,
@@ -17,7 +18,7 @@ type Mode = 'signin' | 'register';
 
 export default function LoginScreen() {
   const { login, register } = useAuth();
-  const { online, resolved } = useConnection();
+  const { online, resolved, settings } = useConnection();
 
   const [mode, setMode] = useState<Mode>('signin');
   const [username, setUsername] = useState('');
@@ -134,11 +135,25 @@ export default function LoginScreen() {
               }}
             />
 
+            {/* A release build starts with no instance configured, and sign-in
+                is impossible until one is set — Settings also owns that field,
+                so the login screen must be able to reach it. Without this the
+                app is unconfigurable on a fresh install (Settings was only
+                reachable from Home, which needs a session). */}
+            <Button
+              label={settings.instanceUrl ? `Server · ${settings.instanceUrl}` : 'Choose your server'}
+              variant="ghost"
+              height={44}
+              onPress={() => {
+                if (navigationRef.isReady()) navigationRef.navigate('Settings');
+              }}
+            />
+
             {!online ? (
               <AppText style={{ ...typeCaption, color: textSecondary, textAlign: 'center' }}>
                 {resolved
-                  ? 'The alarm service did not answer. Check Settings → Connection.'
-                  : 'Looking for the alarm service…'}
+                  ? 'Your instance did not answer. Check Settings → Connection.'
+                  : 'Looking for your instance…'}
               </AppText>
             ) : null}
           </View>