safety(web-dashboard): theme-consistent chart colors, a11y attributes, WS reconnect, loading skeletons

- Replace all hardcoded hex colors in chart components with CSS custom
  properties (getCssVar helper), making charts respect theme changes
- Add scope="col" to all table headers (PositionsTable, OrdersTable,
  BacktestingDashboard trade list)
- Connect form labels to inputs via htmlFor/id pairs (OrderForm,
  BacktestingDashboard)
- Add role="alert" to validation error messages
- Add aria-label to cancel button, progressbar role to backtest progress
- Add WsManager.reconnect() method with backoff reset
- Add Reconnect button to StatusBar when WS disconnected
- Add shimmer skeleton loading states to CandlestickChart and PnLChart

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web-dashboard/src/components/common/StatusBar.tsx

@@ -1,6 +1,7 @@
 import { useWebSocket } from '../../hooks/useWebSocket';
 import { useAuth } from '../../hooks/useAuth';
 import { getTokenClaims } from '../../lib/auth';
+import { wsManager } from '../../lib/websocket';
 
 const EMPTY_TOPICS: string[] = [];
 
@@ -19,7 +20,18 @@ export function StatusBar() {
             }`}
             aria-hidden="true"
           />
-          WS: {connected ? 'Connected' : 'Disconnected'}
+          WS: {connected ? 'Connected' : (
+            <>
+              Disconnected
+              <button
+                onClick={() => wsManager.reconnect()}
+                className="ml-1 px-1.5 py-0.5 rounded text-[var(--color-accent)] hover:bg-[var(--color-accent)]/10 transition-colors"
+                aria-label="Reconnect WebSocket"
+              >
+                Reconnect
+              </button>
+            </>
+          )}
         </span>
         {authenticated && claims && (
           <span>User: {claims.sub}</span>