Widgets: bars countdown widget + unified slate/orange theme (KC-15)

- New EventBarsWidget ("Event Countdown (Bars)") using BarGrid + EventBarsView,
  with a fine "X hr, Y min left" label; registered in the bundle.
- Re-themed every home-screen widget to the shared WidgetTheme (dark slate
  background + brand orange): Day Progress, Tasks Done Today, Event Countdown
  (dots), My Tasks. Lock-screen widgets keep .thinMaterial (system-tinted).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

KisaniCalWidgets/MyTasksWidget.swift

@@ -96,7 +96,7 @@ struct MyTasksView: View {
             HStack(spacing: 6) {
                 Text("Today")
                     .font(.system(size: 18, weight: .bold))
-                    .foregroundColor(Color(red: 0.42, green: 0.5, blue: 0.96))
+                    .foregroundColor(WidgetTheme.accent)
                 Text("\(entry.openCount)")
                     .font(.system(size: 15, weight: .semibold))
                     .foregroundColor(Color(white: 0.5))
@@ -104,7 +104,7 @@ struct MyTasksView: View {
                 Button(intent: AddTaskFromWidgetIntent()) {
                     Image(systemName: "plus")
                         .font(.system(size: 16, weight: .semibold))
-                        .foregroundColor(Color(red: 0.42, green: 0.5, blue: 0.96))
+                        .foregroundColor(WidgetTheme.accent)
                 }
                 .buttonStyle(.plain)
             }
@@ -143,6 +143,6 @@ struct MyTasksView: View {
                 Spacer(minLength: 0)
             }
         }
-        .containerBackground(.black, for: .widget)
+        .containerBackground(WidgetTheme.background, for: .widget)
     }
 }