feat: move difficulty parameters into Smart mode

Group difficulty configuration parameters inside Smart Difficulty mode:
- Digit Range moved from always-visible to Smart mode
- Regrouping Frequency moved from always-visible to Smart mode
- These are difficulty tuning parameters, not general settings

Changes:
- Add DigitRangeSection to top of SmartModeControls
- Add RegroupingFrequencyPanel to bottom of SmartModeControls
- Extract RegroupingFrequencyPanel as standalone component
- Remove both from ConfigPanel's always-visible section

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

apps/web/src/app/create/worksheets/addition/components/config-panel/RegroupingFrequencyPanel.tsx

@@ -0,0 +1,168 @@
+'use client'
+
+import * as Slider from '@radix-ui/react-slider'
+import { css } from '../../../../../../../styled-system/css'
+import { stack } from '../../../../../../../styled-system/patterns'
+import type { WorksheetFormState } from '../../types'
+
+export interface RegroupingFrequencyPanelProps {
+  formState: WorksheetFormState
+  onChange: (updates: Partial<WorksheetFormState>) => void
+  isDark?: boolean
+}
+
+export function RegroupingFrequencyPanel({
+  formState,
+  onChange,
+  isDark = false,
+}: RegroupingFrequencyPanelProps) {
+  return (
+    <div
+      data-section="regrouping"
+      className={css({
+        bg: isDark ? 'gray.800' : 'gray.50',
+        border: '1px solid',
+        borderColor: isDark ? 'gray.600' : 'gray.200',
+        rounded: 'xl',
+        p: '3',
+      })}
+    >
+      <div className={stack({ gap: '2.5' })}>
+        <div
+          className={css({
+            fontSize: 'xs',
+            fontWeight: 'semibold',
+            color: isDark ? 'gray.400' : 'gray.500',
+            textTransform: 'uppercase',
+            letterSpacing: 'wider',
+          })}
+        >
+          Regrouping Frequency
+        </div>
+
+        {/* Current values display */}
+        <div
+          className={css({
+            display: 'flex',
+            justifyContent: 'space-between',
+            fontSize: 'xs',
+            color: isDark ? 'gray.400' : 'gray.600',
+          })}
+        >
+          <div>
+            Both:{' '}
+            <span
+              className={css({
+                color: 'brand.600',
+                fontWeight: 'semibold',
+              })}
+            >
+              {Math.round((formState.pAllStart || 0) * 100)}%
+            </span>
+          </div>
+          <div>
+            Any:{' '}
+            <span
+              className={css({
+                color: 'brand.600',
+                fontWeight: 'semibold',
+              })}
+            >
+              {Math.round((formState.pAnyStart || 0.25) * 100)}%
+            </span>
+          </div>
+        </div>
+
+        {/* Double-thumbed range slider */}
+        <Slider.Root
+          className={css({
+            position: 'relative',
+            display: 'flex',
+            alignItems: 'center',
+            userSelect: 'none',
+            touchAction: 'none',
+            width: 'full',
+            height: '6',
+          })}
+          value={[(formState.pAllStart || 0) * 100, (formState.pAnyStart || 0.25) * 100]}
+          onValueChange={(values) => {
+            onChange({
+              pAllStart: values[0] / 100,
+              pAnyStart: values[1] / 100,
+            })
+          }}
+          min={0}
+          max={100}
+          step={5}
+          minStepsBetweenThumbs={0}
+        >
+          <Slider.Track
+            className={css({
+              position: 'relative',
+              flexGrow: 1,
+              bg: 'gray.200',
+              rounded: 'full',
+              height: '1.5',
+            })}
+          >
+            <Slider.Range
+              className={css({
+                position: 'absolute',
+                bg: 'brand.500',
+                rounded: 'full',
+                height: 'full',
+              })}
+            />
+          </Slider.Track>
+          <Slider.Thumb
+            className={css({
+              display: 'block',
+              width: '3.5',
+              height: '3.5',
+              bg: 'white',
+              boxShadow: '0 2px 4px rgba(0,0,0,0.15)',
+              rounded: 'full',
+              border: '2px solid',
+              borderColor: 'brand.500',
+              cursor: 'pointer',
+              _hover: { transform: 'scale(1.1)' },
+              _focus: {
+                outline: 'none',
+                boxShadow: '0 0 0 3px rgba(59, 130, 246, 0.3)',
+              },
+            })}
+          />
+          <Slider.Thumb
+            className={css({
+              display: 'block',
+              width: '3.5',
+              height: '3.5',
+              bg: 'white',
+              boxShadow: '0 2px 4px rgba(0,0,0,0.15)',
+              rounded: 'full',
+              border: '2px solid',
+              borderColor: 'brand.600',
+              cursor: 'pointer',
+              _hover: { transform: 'scale(1.1)' },
+              _focus: {
+                outline: 'none',
+                boxShadow: '0 0 0 3px rgba(59, 130, 246, 0.3)',
+              },
+            })}
+          />
+        </Slider.Root>
+
+        <div
+          className={css({
+            fontSize: '2xs',
+            color: isDark ? 'gray.400' : 'gray.500',
+            lineHeight: '1.3',
+          })}
+        >
+          Regrouping difficulty at worksheet start (Both = all columns regroup, Any = at least one
+          column regroups)
+        </div>
+      </div>
+    </div>
+  )
+}

apps/web/src/app/create/worksheets/addition/components/config-panel/SmartModeControls.tsx

@@ -25,6 +25,8 @@ import {
 } from '../../difficultyProfiles'
 import type { DisplayRules } from '../../displayRules'
 import { getScaffoldingSummary } from './utils'
+import { RegroupingFrequencyPanel } from './RegroupingFrequencyPanel'
+import { DigitRangeSection } from './DigitRangeSection'
 
 export interface SmartModeControlsProps {
   formState: WorksheetFormState
@@ -74,22 +76,21 @@ export function SmartModeControls({ formState, onChange, isDark = false }: Smart
   }
 
   return (
-    <div
-      data-section="difficulty"
-      className={css({
-        bg: 'gray.50',
-        border: '1px solid',
-        borderColor: 'gray.200',
-        rounded: 'xl',
-        p: '3',
-      })}
-    >
-      <div className={stack({ gap: '2.5' })}>
+    <div data-section="smart-mode" className={stack({ gap: '3' })}>
+      {/* Digit Range */}
+      <DigitRangeSection
+        digitRange={formState.digitRange}
+        onChange={(digitRange) => onChange({ digitRange })}
+        isDark={isDark}
+      />
+
+      {/* Difficulty Level */}
+      <div data-section="difficulty" className={stack({ gap: '2.5' })}>
         <div
           className={css({
             fontSize: 'xs',
             fontWeight: 'semibold',
-            color: 'gray.500',
+            color: isDark ? 'gray.400' : 'gray.500',
             textTransform: 'uppercase',
             letterSpacing: 'wider',
           })}
@@ -1478,6 +1479,9 @@ export function SmartModeControls({ formState, onChange, isDark = false }: Smart
           )
         })()}
       </div>
+
+      {/* Regrouping Frequency */}
+      <RegroupingFrequencyPanel formState={formState} onChange={onChange} isDark={isDark} />
     </div>
   )
 }