refactor: move progressive difficulty toggle below operator section

Move the "Progressive difficulty" toggle to appear immediately after
the "Operator" section in the worksheet configuration panel, before
the "Mode Selector". This creates a more logical flow:

1. Student Name
2. Digit Range
3. Operator
4. Progressive Difficulty
5. Mode Selector
6. Mode-specific controls

Previously, Progressive Difficulty appeared after Mode Selector, which
broke the logical grouping of basic settings before mode selection.

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

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

apps/web/.claude/settings.local.json

@@ -48,7 +48,5 @@
     "ask": []
   },
   "enableAllProjectMcpServers": true,
-  "enabledMcpjsonServers": [
-    "sqlite"
-  ]
+  "enabledMcpjsonServers": ["sqlite"]
 }

apps/web/src/app/create/worksheets/addition/components/ConfigPanel.tsx

@@ -98,13 +98,6 @@ export function ConfigPanel({ formState, onChange, isDark = false }: ConfigPanel
         isDark={isDark}
       />
 
-      {/* Mode Selector */}
-      <ModeSelector
-        currentMode={formState.mode ?? 'smart'}
-        onChange={handleModeChange}
-        isDark={isDark}
-      />
-
       {/* Progressive Difficulty Toggle - Available for all modes */}
       <ProgressiveDifficultyToggle
         interpolate={formState.interpolate}
@@ -112,6 +105,13 @@ export function ConfigPanel({ formState, onChange, isDark = false }: ConfigPanel
         isDark={isDark}
       />
 
+      {/* Mode Selector */}
+      <ModeSelector
+        currentMode={formState.mode ?? 'smart'}
+        onChange={handleModeChange}
+        isDark={isDark}
+      />
+
       {/* Smart Mode Controls */}
       {(!formState.mode || formState.mode === 'smart') && (
         <SmartModeControls formState={formState} onChange={onChange} isDark={isDark} />