fixed client-reported crashes in the pdf viewer, image picker and prosemirror images, mapped webdav errors to user messages and hardened keychain, cache and push stores against io failures

test/widget/prosemirror/pm_image_width_test.dart

@@ -0,0 +1,31 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:marianum_mobile/widget/prosemirror/pm_image_view.dart';
+
+void main() {
+  group('resolvePmImageWidth', () {
+    test('returns null without a width attribute', () {
+      expect(resolvePmImageWidth(null, 300), isNull);
+    });
+
+    test('returns null for unparseable widths', () {
+      expect(resolvePmImageWidth('auto', 300), isNull);
+    });
+
+    test('resolves px, %, em and rem', () {
+      expect(resolvePmImageWidth('120px', 300), 120);
+      expect(resolvePmImageWidth('50%', 300), 150);
+      expect(resolvePmImageWidth('2em', 300), 32);
+      expect(resolvePmImageWidth('2rem', 300), 32);
+    });
+
+    test('caps at the available width and floors at one pixel', () {
+      expect(resolvePmImageWidth('900px', 300), 300);
+      expect(resolvePmImageWidth('0px', 300), 1);
+    });
+
+    test('survives zero or sub-pixel available width', () {
+      expect(resolvePmImageWidth('50%', 0), isNull);
+      expect(resolvePmImageWidth('120px', 0.5), isNull);
+    });
+  });
+}