fix: remove hardcoded default server URL from mobile app

ushadow/mobile/.env.example

@@ -0,0 +1,11 @@
+# Ushadow Mobile App Environment Variables
+# Copy this file to .env and customize for your build
+#
+# Note: Variables must be prefixed with EXPO_PUBLIC_ to be accessible in the app
+
+# Default server URL (optional)
+# If set, this will pre-fill the server URL field on first login
+# Users can still change it during login
+# Format: https://{your-tailscale-host}
+# Example: https://blue.spangled-kettle.ts.net
+EXPO_PUBLIC_DEFAULT_SERVER_URL=

ushadow/mobile/README.md

@@ -44,6 +44,38 @@ eas build --profile preview --platform ios      # Requires Apple Developer accou
 
 ---
 
+## Build Configuration
+
+### Setting a Default Server URL (Optional)
+
+You can pre-configure a default server URL that will be filled in automatically when users first open the app. This is useful when distributing the app to your team.
+
+**Option 1: Environment Variable (Recommended)**
+
+Create a `.env` file in the `ushadow/mobile/` directory:
+
+```bash
+# Copy the example file
+cp .env.example .env
+
+# Edit with your server URL
+echo 'EXPO_PUBLIC_DEFAULT_SERVER_URL=https://your-server.ts.net' > .env
+```
+
+Then build the app normally. The URL will be embedded at build time.
+
+**Option 2: EAS Build Secrets**
+
+For EAS builds, set the environment variable in your EAS secrets:
+
+```bash
+eas secret:create --name EXPO_PUBLIC_DEFAULT_SERVER_URL --value "https://your-server.ts.net"
+```
+
+**Note:** Users can always change the server URL during login, even if a default is set. The URL they use is saved for future logins.
+
+---
+
 ## Detailed Setup Instructions
 
 ### Prerequisites

ushadow/mobile/app/_utils/authStorage.ts

@@ -143,7 +143,10 @@ export function appendTokenToUrl(wsUrl: string, token: string): string {
 
 /**
  * Get the default server URL.
- * Returns user-configured default if set, otherwise returns app config default.
+ * Priority:
+ * 1. User-saved default (from "Save as default" checkbox)
+ * 2. Build-time default from EXPO_PUBLIC_DEFAULT_SERVER_URL env var
+ * 3. Empty string (user must enter URL manually)
  */
 export async function getDefaultServerUrl(): Promise<string> {
   try {
@@ -154,6 +157,7 @@ export async function getDefaultServerUrl(): Promise<string> {
   } catch (error) {
     console.error('[AuthStorage] Failed to get default server URL:', error);
   }
+  // Fall back to build-time default from env var (or empty string)
   return AppConfig.DEFAULT_SERVER_URL;
 }
 
@@ -172,7 +176,8 @@ export async function setDefaultServerUrl(url: string): Promise<void> {
 }
 
 /**
- * Clear the custom default server URL (revert to app config default).
+ * Clear the custom default server URL.
+ * After clearing, users will need to enter the URL manually on next login.
  */
 export async function clearDefaultServerUrl(): Promise<void> {
   try {
@@ -186,7 +191,7 @@ export async function clearDefaultServerUrl(): Promise<void> {
 
 /**
  * Get the effective server URL to use.
- * Priority: stored API URL > custom default > app config default
+ * Priority: stored API URL from login > saved default server URL > empty string
  */
 export async function getEffectiveServerUrl(): Promise<string> {
   // First check if there's a stored API URL from login

ushadow/mobile/app/components/LoginScreen.tsx

@@ -25,7 +25,12 @@ import {
   ScrollView,
 } from 'react-native';
 import { colors, theme, spacing, borderRadius, fontSize } from '../theme';
-import { saveAuthToken, saveApiUrl } from '../_utils/authStorage';
+import {
+  saveAuthToken,
+  saveApiUrl,
+  getDefaultServerUrl,
+  setDefaultServerUrl,
+} from '../_utils/authStorage';
 
 interface LoginScreenProps {
   visible: boolean;

ushadow/mobile/app/config.ts

@@ -2,19 +2,27 @@
  * App Configuration
  *
  * Central configuration for the Ushadow mobile app.
- * The default server URL can be changed here or overridden by the user during setup.
+ * Configuration is read from environment variables at build time.
+ *
+ * To set a default server URL for your build:
+ * 1. Create a .env file in ushadow/mobile/
+ * 2. Add: EXPO_PUBLIC_DEFAULT_SERVER_URL=https://your-server.ts.net
+ * 3. Build the app
+ *
+ * See README.md for more details.
  */
 
 export const AppConfig = {
   /**
    * Default server URL.
-   * This is used as the initial value when the app is first installed.
-   * Users can change this in the login screen.
+   * Read from EXPO_PUBLIC_DEFAULT_SERVER_URL environment variable.
+   * If not set, users enter the URL manually during first login.
+   * Once logged in, the URL is persisted in AsyncStorage.
    *
    * Format: https://{your-tailscale-host}
    * Example: https://blue.spangled-kettle.ts.net
    */
-  DEFAULT_SERVER_URL: 'https://ushadow.wolf-tawny.ts.net',
+  DEFAULT_SERVER_URL: process.env.EXPO_PUBLIC_DEFAULT_SERVER_URL || '',
 
   /**
    * App version info