refactor: design critique fixes for account pages

- Admin accounts: replace dense card grid with compact DataTable
- Account settings: remove redundant hero card, stat grid, header pills
- Fix bg-accent (orange) misuse on decorative elements across 7 files
- Add ConfirmButton for destructive actions (deactivate, remove member)
- Replace single-field modals with inline editing (plan, trial)
- Add contextual help: display code tooltip, improved empty states
- Non-owner aside explanation for hidden owner-only sections
- Admin sidebar: group 11 items into 5 labeled sections
- Rename UsersPage.tsx → AccountsPage.tsx to match route
- Fix border radius consistency, hide zero-count badges

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

frontend/src/components/common/ConfirmButton.tsx

@@ -0,0 +1,69 @@
+import { useCallback, useEffect, useRef, useState } from 'react'
+import { cn } from '@/lib/utils'
+
+interface ConfirmButtonProps {
+  onConfirm: () => void
+  children: React.ReactNode
+  confirmLabel?: string
+  className?: string
+  confirmClassName?: string
+  timeoutMs?: number
+  'aria-label'?: string
+}
+
+/**
+ * Two-click inline confirm button.
+ * First click arms the button (shows confirm state).
+ * Second click executes the action.
+ * Auto-resets after timeoutMs (default 3000ms).
+ */
+export function ConfirmButton({
+  onConfirm,
+  children,
+  confirmLabel = 'Confirm?',
+  className,
+  confirmClassName,
+  timeoutMs = 3000,
+  'aria-label': ariaLabel,
+}: ConfirmButtonProps) {
+  const [armed, setArmed] = useState(false)
+  const timerRef = useRef<ReturnType<typeof setTimeout> | null>(null)
+
+  const reset = useCallback(() => {
+    setArmed(false)
+    if (timerRef.current) {
+      clearTimeout(timerRef.current)
+      timerRef.current = null
+    }
+  }, [])
+
+  useEffect(() => {
+    return () => {
+      if (timerRef.current) clearTimeout(timerRef.current)
+    }
+  }, [])
+
+  const handleClick = () => {
+    if (armed) {
+      reset()
+      onConfirm()
+    } else {
+      setArmed(true)
+      timerRef.current = setTimeout(reset, timeoutMs)
+    }
+  }
+
+  return (
+    <button
+      type="button"
+      onClick={handleClick}
+      onBlur={reset}
+      aria-label={ariaLabel}
+      className={cn(armed ? confirmClassName : className)}
+    >
+      {armed ? confirmLabel : children}
+    </button>
+  )
+}
+
+export default ConfirmButton