feat(dev): centraliser l'IP LAN dans android/local.properties — source unique

- build.gradle : tâche generateDevConfig qui propage dev.host vers
  network_security_config.xml et lib/core/config/local_config.dart à chaque build
- environment.dart : import kDevHost depuis local_config.dart pour les URLs dev
  (apiBaseUrl, keycloakBaseUrl, wsBaseUrl) — plus de constante IP hardcodée
- local_config.dart : fichier auto-généré (ne pas éditer directement)
- network_security_config.xml : autorisation cleartext pour 192.168.1.13

Pour changer l'IP : modifier uniquement android/local.properties → dev.host

android/app/build.gradle

@@ -5,6 +5,63 @@ plugins {
     id "dev.flutter.flutter-gradle-plugin"
 }
 
+// ── Dev Host — source unique : android/local.properties → dev.host ───────────
+def localProps = new Properties()
+def localPropsFile = rootProject.file('local.properties')
+if (localPropsFile.exists()) localPropsFile.withInputStream { localProps.load(it) }
+def devHost = localProps.getProperty('dev.host', '10.0.2.2')
+
+task generateDevConfig {
+    description = 'Generates network_security_config.xml and local_config.dart from local.properties'
+    group = 'UnionFlow'
+    inputs.property('devHost', devHost)
+    outputs.files(
+        file("src/main/res/xml/network_security_config.xml"),
+        rootProject.file("../lib/core/config/local_config.dart")
+    )
+    doLast {
+        def xmlContent = """\
+<?xml version="1.0" encoding="utf-8"?>
+<network-security-config>
+    <!-- Production: cleartext disabled by default -->
+    <base-config cleartextTrafficPermitted="false">
+        <trust-anchors>
+            <certificates src="system"/>
+        </trust-anchors>
+    </base-config>
+    <!-- Dev local - single source: android/local.properties -> dev.host -->
+    <domain-config cleartextTrafficPermitted="true">
+        <domain includeSubdomains="true">${devHost}</domain>
+        <domain includeSubdomains="true">localhost</domain>
+        <domain includeSubdomains="true">10.0.2.2</domain>
+        <domain includeSubdomains="true">127.0.0.1</domain>
+    </domain-config>
+</network-security-config>"""
+
+        def dartContent = """\
+// AUTO-GENERATED by build.gradle - DO NOT EDIT
+// Edit android/local.properties (dev.host) instead.
+// ignore_for_file: prefer_single_quotes
+const String kDevHost = '${devHost}';
+"""
+
+        // Write with explicit UTF-8 encoding (avoids Windows-1252 on French systems)
+        file("src/main/res/xml/network_security_config.xml")
+            .newWriter('UTF-8').withWriter { w -> w << xmlContent }
+        rootProject.file("../lib/core/config/local_config.dart")
+            .newWriter('UTF-8').withWriter { w -> w << dartContent }
+    }
+}
+preBuild.dependsOn generateDevConfig
+
+// local_config.dart is consumed by Flutter compile tasks — declare explicit dependency
+tasks.configureEach { task ->
+    if (task.name.startsWith('compileFlutterBuild')) {
+        task.dependsOn generateDevConfig
+    }
+}
+// ─────────────────────────────────────────────────────────────────────────────
+
 android {
     namespace = "dev.lions.unionflow_mobile_apps"
     compileSdk = 36