simplified code across the app and consolidated duplicated helpers

lib/widget/prosemirror/pm_image_view.dart

@@ -123,19 +123,14 @@ class PmImageView extends StatelessWidget {
 
   double? _resolveWidth(String? width, double available) {
     if (width == null) return null;
-    final match = RegExp(r'^(\d+(?:\.\d+)?)(px|%|em|rem)$').firstMatch(width);
-    if (match == null) return null;
-    final value = double.parse(match.group(1)!);
-    final double resolved;
-    switch (match.group(2)) {
-      case '%':
-        resolved = available * value / 100;
-      case 'em':
-      case 'rem':
-        resolved = value * 16;
-      default:
-        resolved = value;
-    }
+    final length = parsePmCssLength(width);
+    if (length == null) return null;
+    final value = length.value;
+    final resolved = switch (length.unit) {
+      '%' => available * value / 100,
+      'em' || 'rem' => value * 16,
+      _ => value,
+    };
     return resolved.clamp(1, available);
   }
 }

lib/widget/prosemirror/pm_node.dart

@@ -325,3 +325,12 @@ class PmUnknown extends PmNode {
 
   const PmUnknown({required this.rawType, this.children = const []});
 }
+
+final RegExp _cssLength = RegExp(r'^(\d+(?:\.\d+)?)(px|%|em|rem)$');
+
+/// Splits a CSS length like `12px` / `1.5em` / `50%` into value and unit.
+({double value, String unit})? parsePmCssLength(String raw) {
+  final match = _cssLength.firstMatch(raw);
+  if (match == null) return null;
+  return (value: double.parse(match.group(1)!), unit: match.group(2)!);
+}

lib/widget/prosemirror/pm_rich_text.dart

@@ -152,22 +152,15 @@ class _PmRichTextState extends State<PmRichText> {
 
   double? _fontSize(dynamic raw, double base) {
     if (raw is! String) return null;
-    final match = RegExp(r'^(\d+(?:\.\d+)?)(px|rem|em|%)$').firstMatch(raw);
-    if (match == null) return null;
-    final value = double.parse(match.group(1)!);
-    final double size;
-    switch (match.group(2)) {
-      case 'px':
-        size = value;
-      case 'rem':
-        size = value * 16;
-      case 'em':
-        size = base * value;
-      case '%':
-        size = base * value / 100;
-      default:
-        return null;
-    }
+    final length = parsePmCssLength(raw);
+    if (length == null) return null;
+    final value = length.value;
+    final size = switch (length.unit) {
+      'px' => value,
+      'rem' => value * 16,
+      'em' => base * value,
+      _ => base * value / 100,
+    };
     return size.clamp(8, 72);
   }
 

lib/widget/prosemirror/pm_table_view.dart

@@ -195,7 +195,7 @@ class _PmTableViewState extends State<PmTableView> {
     required bool left,
     required bool visible,
   }) {
-    final dark = Theme.of(context).brightness == Brightness.dark;
+    final dark = AppTheme.isDarkMode(context);
     final color = Colors.black.withValues(alpha: dark ? 0.28 : 0.12);
     return Positioned(
       top: 0,