feat(theme): Querya Light preset in main shell (#51)

docs/theme.md

@@ -55,7 +55,7 @@ flowchart TB
 ## Built-in presets
 
 - **Querya Dark** — default (`QueryaThemePreset.queryaDark`)
-- **Querya Light** — light UI (`QueryaThemePreset.queryaLight`)
+- **Querya Light** — built-in light UI (`QueryaThemePreset.queryaLight`); slate canvas, cyan accent, WCAG AA body text
 - **Imported** — after a VS Code file is imported (`QueryaThemePreset.imported`)
 
 Access tokens in widgets:

lib/core/theme/querya_workbench_theme.dart

@@ -51,7 +51,7 @@ class QueryaWorkbenchTheme {
     gitUntracked: Color(0xFF2EB88A),
   );
 
-  /// Placeholder light preset (#51 will refine).
+  /// Built-in light preset (slate-like canvas, cyan brand accent).
   static const QueryaWorkbenchTheme lightDefault = QueryaWorkbenchTheme(
     canvas: Color(0xFFFAFAFA),
     surface: Color(0xFFFFFFFF),

lib/features/main_screen/main_screen.dart

@@ -16,8 +16,8 @@ import 'package:flutter/material.dart' as material
         Widget,
         RepaintBoundary;
 import 'package:querya_desktop/core/storage/local_db.dart';
-import 'package:querya_desktop/core/theme/app_theme.dart';
 import 'package:querya_desktop/core/theme/querya_theme_scope.dart';
+import 'package:shadcn_flutter/shadcn_flutter.dart';
 import 'package:querya_desktop/features/connections/connection_creation_flow.dart';
 import 'package:querya_desktop/features/connections/connections_panel.dart';
 import 'package:querya_desktop/shared/widgets/widgets.dart';
@@ -127,37 +127,34 @@ class _MainScreenState extends State<MainScreen> {
 
   @override
   material.Widget build(material.BuildContext context) {
-    final theme = AppTheme.dark.colorScheme;
+    final scheme = Theme.of(context).colorScheme;
     return material.Scaffold(
-      backgroundColor: theme.background,
-      body: Theme(
-        data: AppTheme.dark,
-        child: WindowBorder(
-          color: theme.border.withValues(alpha: 0.35),
-          width: 1,
-          child: Column(
-            children: [
-              _CustomTitleBar(
-                theme: theme,
-                onNewDatabaseConnection: _onNewDatabaseConnectionFromMenu,
-              ),
-              Divider(height: 1, color: theme.border.withValues(alpha: 0.22)),
-              Expanded(
-                child: _MainContentSplit(
-                  connectionsPanelKey: _connectionsPanelKey,
-                  workspace: _workspace,
-                  onConnectionSelected: _onConnectionSelected,
-                  onPostgresObjectSelected: _onPostgresObjectSelected,
-                  onMysqlObjectSelected: _onMysqlObjectSelected,
-                  onRedisDatabaseSelected: _onRedisDatabaseSelected,
-                  onMongoDBDatabaseSelected: _onMongoDBDatabaseSelected,
-                  onPostgresOpenSqlWorkspace: _onPostgresOpenSqlWorkspace,
-                  onMysqlOpenSqlWorkspace: _onMysqlOpenSqlWorkspace,
-                  onRequestNewConnection: _openNewConnectionFromHero,
-                ),
+      backgroundColor: scheme.background,
+      body: WindowBorder(
+        color: scheme.border.withValues(alpha: 0.35),
+        width: 1,
+        child: Column(
+          children: [
+            _CustomTitleBar(
+              theme: scheme,
+              onNewDatabaseConnection: _onNewDatabaseConnectionFromMenu,
+            ),
+            Divider(height: 1, color: scheme.border.withValues(alpha: 0.22)),
+            Expanded(
+              child: _MainContentSplit(
+                connectionsPanelKey: _connectionsPanelKey,
+                workspace: _workspace,
+                onConnectionSelected: _onConnectionSelected,
+                onPostgresObjectSelected: _onPostgresObjectSelected,
+                onMysqlObjectSelected: _onMysqlObjectSelected,
+                onRedisDatabaseSelected: _onRedisDatabaseSelected,
+                onMongoDBDatabaseSelected: _onMongoDBDatabaseSelected,
+                onPostgresOpenSqlWorkspace: _onPostgresOpenSqlWorkspace,
+                onMysqlOpenSqlWorkspace: _onMysqlOpenSqlWorkspace,
+                onRequestNewConnection: _openNewConnectionFromHero,
               ),
-            ],
-          ),
+            ),
+          ],
         ),
       ),
     );

test/core/theme/querya_light_theme_test.dart

@@ -0,0 +1,64 @@
+import 'dart:math' as math;
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:querya_desktop/core/theme/querya_color_scheme.dart';
+import 'package:querya_desktop/core/theme/querya_theme.dart';
+import 'package:shadcn_flutter/shadcn_flutter.dart';
+
+void main() {
+  group('QueryaTheme.lightDefault', () {
+    test('colorScheme differs from dark preset', () {
+      final light = QueryaTheme.lightDefault.colorScheme;
+      final dark = QueryaTheme.darkDefault.colorScheme;
+      expect(light.background, isNot(dark.background));
+      expect(light.foreground, isNot(dark.foreground));
+      expect(light.brightness, Brightness.light);
+    });
+
+    test('QueryaColorScheme.light matches lightDefault', () {
+      expect(
+        QueryaColorScheme.light.background,
+        QueryaTheme.lightDefault.colorScheme.background,
+      );
+    });
+
+    test('primary text on canvas meets WCAG AA contrast (4.5:1)', () {
+      final w = QueryaTheme.lightDefault.workbench;
+      final ratio = contrastRatio(w.canvas, const Color(0xFF0F172A));
+      expect(ratio, greaterThanOrEqualTo(4.5));
+    });
+
+    test('editor foreground on editor background meets WCAG AA', () {
+      final e = QueryaTheme.lightDefault.editor;
+      final ratio = contrastRatio(e.background, e.foreground);
+      expect(ratio, greaterThanOrEqualTo(4.5));
+    });
+
+    test('toShadcnThemeData uses light brightness', () {
+      final td = QueryaTheme.lightDefault.toShadcnThemeData();
+      expect(td.brightness, Brightness.light);
+      expect(td.colorScheme.primary, QueryaTheme.lightDefault.workbench.accent);
+    });
+  });
+}
+
+/// Relative luminance contrast per WCAG 2.1.
+double contrastRatio(Color a, Color b) {
+  final l1 = _relativeLuminance(a);
+  final l2 = _relativeLuminance(b);
+  final lighter = math.max(l1, l2);
+  final darker = math.min(l1, l2);
+  return (lighter + 0.05) / (darker + 0.05);
+}
+
+double _relativeLuminance(Color c) {
+  double channel(double v) {
+    final normalized = v <= 0.03928 ? v / 12.92 : math.pow((v + 0.055) / 1.055, 2.4).toDouble();
+    return normalized;
+  }
+
+  final r = channel(c.r);
+  final g = channel(c.g);
+  final b = channel(c.b);
+  return 0.2126 * r + 0.7152 * g + 0.0722 * b;
+}