feat: Handy - Platz fuer Statusleiste, randlose Bild-Vollansicht mit Gesten, groessere Medien im Chat

Bernds Beta-Feedback:
- main.dart: edgeToEdge statt immersiveSticky (Statusleiste schob sich ueber
  den Inhalt); MobileShell mit SafeArea + Statusleisten-Symbolen passend
  zum Theme, Hintergrund bg1 = Kopfzeilenfarbe.
- MediaViewer: Handy randlos auf Schwarz (vorher 24-px-Rand, halbtransparent);
  Tippen neben das Bild schliesst, aufs Bild blendet Leiste ein/aus; Wischen
  hoch/runter schliesst (nur ohne Zoom, ueber InteractiveViewer-Callbacks,
  kein Gestenkonflikt mit Zwei-Finger-Zoom); Doppeltipp zoomt an der Stelle.
- Chat: Bilder auf dem Handy bis halbe Bildschirmhoehe statt fest 320 px;
  Videos im echten Seitenverhaeltnis statt fest 16:9.
- UI-Durchlauf integration_test/mobile_ui_screens_test.dart (Handy-Format,
  Testprofil, Screenshots nach build/ui_screens/) + Testinhalte-Helfer
  test/live_ui_fixture_test.dart; scripts/test.ps1 -Ui.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

pubspec.lock

@@ -350,6 +350,11 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  flutter_driver:
+    dependency: transitive
+    description: flutter
+    source: sdk
+    version: "0.0.0"
   flutter_launcher_icons:
     dependency: "direct dev"
     description:
@@ -517,6 +522,11 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "4.0.0"
+  fuchsia_remote_debug_protocol:
+    dependency: transitive
+    description: flutter
+    source: sdk
+    version: "0.0.0"
   glob:
     dependency: transitive
     description:
@@ -581,6 +591,11 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "4.8.0"
+  integration_test:
+    dependency: "direct dev"
+    description: flutter
+    source: sdk
+    version: "0.0.0"
   intl:
     dependency: "direct main"
     description:
@@ -1005,6 +1020,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "3.6.0"
+  process:
+    dependency: transitive
+    description:
+      name: process
+      sha256: "4242ba3508d37e01808bdf71ad1d5bb93a8d671bf2e7450e6b1b353fb0808891"
+      url: "https://pub.dev"
+    source: hosted
+    version: "5.0.6"
   protobuf:
     dependency: transitive
     description:
@@ -1274,6 +1297,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.4.1"
+  sync_http:
+    dependency: transitive
+    description:
+      name: sync_http
+      sha256: "7f0cd72eca000d2e026bcd6f990b81d0ca06022ef4e32fb257b30d3d1014a961"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.3.1"
   synchronized:
     dependency: transitive
     description:
@@ -1515,6 +1546,14 @@ packages:
       url: "https://github.com/google/webcrypto.dart.git"
     source: git
     version: "0.6.0"
+  webdriver:
+    dependency: transitive
+    description:
+      name: webdriver
+      sha256: "28b82ec894fed45dd71c23ba62d1af973ed97dd59a4f5790a4d38b0b13e5657e"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.2.0"
   webrtc_interface:
     dependency: "direct main"
     description: