feat: add comprehensive game configuration system

Add a centralized game configuration system that allows customizable
scoring mechanics and game rules. Users can now set default game
configurations that persist across sessions, and individual quizzes
can have their own configuration overrides.

## New Features

### Game Configuration Options
- Shuffle Questions: Randomize question order when starting a game
- Shuffle Answers: Randomize answer positions for each question
- Host Participates: Toggle whether the host plays as a competitor
  or spectates (host now shows as 'Spectator' when not participating)
- Streak Bonus: Multiplied points for consecutive correct answers,
  with configurable threshold and multiplier values
- Comeback Bonus: Extra points for players ranked below top 3
- Wrong Answer Penalty: Deduct percentage of max points for incorrect
  answers (configurable percentage)
- First Correct Bonus: Extra points for the first player to answer
  correctly on each question

### Default Settings Management
- New Settings icon in landing page header (authenticated users only)
- DefaultConfigModal for editing user-wide default game settings
- Default configs are loaded when creating new quizzes
- Defaults persist to database via new user API endpoints

### Reusable UI Components
- GameConfigPanel: Comprehensive toggle-based settings panel with
  expandable sub-options, tooltips, and suggested values based on
  question count
- DefaultConfigModal: Modal wrapper for editing default configurations

## Technical Changes

### Frontend
- New useUserConfig hook for fetching/saving user default configurations
- QuizEditor now uses GameConfigPanel instead of inline toggle checkboxes
- GameScreen handles spectator mode with disabled answer buttons
- Updated useGame hook with new scoring calculations and config state
- Improved useAuthenticatedFetch with deduped silent refresh and
  redirect-once pattern to prevent multiple auth redirects

### Backend
- Added game_config column to quizzes table (JSON storage)
- Added default_game_config column to users table
- New PATCH endpoint for quiz config updates: /api/quizzes/:id/config
- New PUT endpoint for user defaults: /api/users/me/default-config
- Auto-migration in connection.ts for existing databases

### Scoring System
- New calculatePoints() function in constants.ts handles all scoring
  logic including streaks, comebacks, penalties, and first-correct bonus
- New calculateBasePoints() for time-based point calculation
- New getPlayerRank() helper for comeback bonus eligibility

### Tests
- Added tests for DefaultConfigModal component
- Added tests for GameConfigPanel component
- Added tests for QuizEditor config integration
- Added tests for useUserConfig hook
- Updated API tests for new endpoints

## Type Changes
- Added GameConfig interface with all configuration options
- Added DEFAULT_GAME_CONFIG constant with sensible defaults
- Quiz type now includes optional config property

components/Landing.tsx

@@ -1,11 +1,13 @@
 import React, { useState, useEffect } from 'react';
 import { motion, AnimatePresence } from 'framer-motion';
-import { BrainCircuit, Loader2, Play, PenTool, BookOpen, Upload, X, FileText, Image, ScanText, Sparkles } from 'lucide-react';
+import { BrainCircuit, Loader2, Play, PenTool, BookOpen, Upload, X, FileText, Image, ScanText, Sparkles, Settings } from 'lucide-react';
 import { useAuth } from 'react-oidc-context';
 import { AuthButton } from './AuthButton';
 import { QuizLibrary } from './QuizLibrary';
+import { DefaultConfigModal } from './DefaultConfigModal';
 import { useQuizLibrary } from '../hooks/useQuizLibrary';
-import type { Quiz } from '../types';
+import { useUserConfig } from '../hooks/useUserConfig';
+import type { Quiz, GameConfig } from '../types';
 
 type GenerateMode = 'topic' | 'document';
 
@@ -31,10 +33,14 @@ export const Landing: React.FC<LandingProps> = ({ onGenerate, onCreateManual, on
   const [questionCount, setQuestionCount] = useState(10);
   const [isDragging, setIsDragging] = useState(false);
   const [useOcr, setUseOcr] = useState(false);
+  const [defaultConfigOpen, setDefaultConfigOpen] = useState(false);
+  const [editingDefaultConfig, setEditingDefaultConfig] = useState<GameConfig | null>(null);
   
   const hasImageFile = selectedFiles.some(f => f.type.startsWith('image/'));
   const hasDocumentFile = selectedFiles.some(f => !f.type.startsWith('image/') && !['application/pdf', 'text/plain', 'text/markdown', 'text/csv', 'text/html'].includes(f.type));
   const showOcrOption = hasImageFile || hasDocumentFile;
+
+  const { defaultConfig, saving: savingConfig, saveDefaultConfig } = useUserConfig();
   
   const { 
     quizzes, 
@@ -132,7 +138,19 @@ export const Landing: React.FC<LandingProps> = ({ onGenerate, onCreateManual, on
 
   return (
     <div className="flex flex-col items-center justify-center min-h-screen p-4 text-center relative">
-      <div className="absolute top-4 right-4">
+      <div className="absolute top-4 right-4 flex items-center gap-2">
+        {auth.isAuthenticated && (
+          <button
+            onClick={() => {
+              setEditingDefaultConfig(defaultConfig);
+              setDefaultConfigOpen(true);
+            }}
+            className="p-2.5 bg-white/90 hover:bg-white rounded-xl shadow-md hover:shadow-lg transition-all text-gray-600 hover:text-theme-primary"
+            title="Default Game Settings"
+          >
+            <Settings size={20} />
+          </button>
+        )}
         <AuthButton />
       </div>
       <motion.div 
@@ -416,6 +434,24 @@ export const Landing: React.FC<LandingProps> = ({ onGenerate, onCreateManual, on
         onDeleteQuiz={deleteQuiz}
         onRetry={retryLibrary}
       />
+
+      <DefaultConfigModal
+        isOpen={defaultConfigOpen}
+        onClose={() => {
+          setDefaultConfigOpen(false);
+          setEditingDefaultConfig(null);
+        }}
+        config={editingDefaultConfig || defaultConfig}
+        onChange={setEditingDefaultConfig}
+        onSave={async () => {
+          if (editingDefaultConfig) {
+            await saveDefaultConfig(editingDefaultConfig);
+            setDefaultConfigOpen(false);
+            setEditingDefaultConfig(null);
+          }
+        }}
+        saving={savingConfig}
+      />
     </div>
   );
 };