Phase 1: Style refinements and component tweaks from Storybook review

Theme & styling:
- Add custom "inspector" color palette with dark navy primary
- Change primaryShade to { light: 7, dark: 8 }
- Add Input theme override to apply --inspector-input-background globally
- Add --inspector-input-background token (white in light, dark-9 in dark)
- Override --mantine-color-body in dark mode via cssVariablesResolver
  in both main.tsx and Storybook preview.tsx
- Add dark-mode CSS overrides for Select dropdown and option hover
- Add dark-mode CSS override for Accordion control hover
- Rename CSS variable --inspector-status-failed → --inspector-status-error

Component changes:
- CopyButton: increase icon font size to 24px, use --inspector-text-primary
  for high-contrast color (black/white per theme)
- TaskControls: remove onClearHistory (moved to TaskListPanel), fix Select
  clear button not disappearing by passing null instead of undefined
- TaskListPanel: add onClearCompleted callback, render "Clear" button
  next to Completed section header
- HistoryListPanel: move "Clear" button from toolbar to History section
  header, rename from "Clear All"

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

clients/web/src/main.tsx

@@ -1,6 +1,6 @@
 import { StrictMode } from "react";
 import { createRoot } from "react-dom/client";
-import { MantineProvider } from "@mantine/core";
+import { MantineProvider, type CSSVariablesResolver } from "@mantine/core";
 import { Notifications } from "@mantine/notifications";
 import "@mantine/core/styles.css";
 import "@mantine/notifications/styles.css";
@@ -8,9 +8,21 @@ import "./App.css";
 import { theme } from "./theme/theme";
 import App from "./App";
 
+const resolver: CSSVariablesResolver = () => ({
+  variables: {},
+  light: {},
+  dark: {
+    "--mantine-color-body": "var(--mantine-color-blue-9)",
+  },
+});
+
 createRoot(document.getElementById("root")!).render(
   <StrictMode>
-    <MantineProvider theme={theme} defaultColorScheme="auto">
+    <MantineProvider
+      theme={theme}
+      defaultColorScheme="auto"
+      cssVariablesResolver={resolver}
+    >
       <Notifications position="top-right" />
       <App />
     </MantineProvider>