feat(dees-button-group): add new button group component with demo and styling

fix(dees-chart-area): improve real-time updates and chart element handling
fix(dees-chart-log): refactor demo to store log element reference
chore: update dependencies in package.json and pnpm-lock.yaml

readme.hints.md

@@ -25,6 +25,7 @@
 - Methods:
   - `updateSeries()`: Update chart data
   - `appendData()`: Add new data points to existing series
+- Demo uses global reference to access chart element (window.__demoChartElement)
 
 ### dees-chart-log  
 - Server log viewer component (not a chart despite the name)
@@ -40,4 +41,21 @@
   - Light/dark theme support
 - Demo includes realistic server log simulation
 - Note: In demos, buttons use `@clicked` event (not `@click`)
-- Demo uses global reference to access log element (window.__demoLogElement)
+- Demo uses global reference to access log element (window.__demoLogElement)
+
+## UI Components
+
+### dees-button-group
+- Groups multiple buttons together with a unified background
+- Properties:
+  - `label`: Optional label text displayed before the buttons
+  - `direction`: 'horizontal' | 'vertical' layout
+- Features:
+  - Light/dark theme support
+  - Flexible layout with proper spacing
+  - Works with all button types (normal, highlighted, success, danger)
+- Use cases:
+  - View mode selectors
+  - Action grouping
+  - Navigation options
+  - Filter controls