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/components/elements/CopyButton/CopyButton.tsx

@@ -15,8 +15,9 @@ export function CopyButton({ value }: CopyButtonProps) {
         <Tooltip label={copied ? "Copied" : "Copy"}>
           <ActionIcon
             variant="subtle"
-            color={copied ? "green" : "gray"}
+            color={copied ? "green" : "var(--inspector-text-primary)"}
             onClick={copy}
+            fz={24}
           >
             {copied ? "\u2713" : "\u2398"}
           </ActionIcon>