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/DefaultConfigModal.tsx

@@ -0,0 +1,95 @@
+import React from 'react';
+import { motion } from 'framer-motion';
+import { X, Settings, Loader2 } from 'lucide-react';
+import { GameConfigPanel } from './GameConfigPanel';
+import { useBodyScrollLock } from '../hooks/useBodyScrollLock';
+import type { GameConfig } from '../types';
+
+interface DefaultConfigModalProps {
+  isOpen: boolean;
+  onClose: () => void;
+  config: GameConfig;
+  onChange: (config: GameConfig) => void;
+  onSave: () => void;
+  saving: boolean;
+}
+
+export const DefaultConfigModal: React.FC<DefaultConfigModalProps> = ({
+  isOpen,
+  onClose,
+  config,
+  onChange,
+  onSave,
+  saving,
+}) => {
+  useBodyScrollLock(isOpen);
+
+  if (!isOpen) return null;
+
+  return (
+    <motion.div
+      initial={{ opacity: 0 }}
+      animate={{ opacity: 1 }}
+      exit={{ opacity: 0 }}
+      className="fixed inset-0 bg-black/50 flex items-center justify-center z-50 p-4"
+      onClick={onClose}
+    >
+      <motion.div
+        initial={{ scale: 0.9, opacity: 0 }}
+        animate={{ scale: 1, opacity: 1 }}
+        exit={{ scale: 0.9, opacity: 0 }}
+        className="bg-white rounded-2xl max-w-lg w-full shadow-xl max-h-[90vh] overflow-hidden flex flex-col"
+        onClick={(e) => e.stopPropagation()}
+      >
+        <div className="p-6 border-b border-gray-100 flex items-center justify-between bg-gradient-to-r from-theme-primary to-purple-600">
+          <div className="flex items-center gap-3 text-white">
+            <div className="p-2 bg-white/20 rounded-xl">
+              <Settings size={24} />
+            </div>
+            <div>
+              <h2 className="text-xl font-black">Default Game Settings</h2>
+              <p className="text-sm opacity-80">Applied to all new quizzes</p>
+            </div>
+          </div>
+          <button
+            onClick={onClose}
+            className="p-2 hover:bg-white/20 rounded-xl transition text-white"
+          >
+            <X size={24} />
+          </button>
+        </div>
+
+        <div className="p-6 overflow-y-auto flex-1 bg-gray-50">
+          <GameConfigPanel
+            config={config}
+            onChange={onChange}
+            questionCount={10}
+          />
+        </div>
+
+        <div className="p-6 border-t border-gray-100 flex gap-3">
+          <button
+            onClick={onClose}
+            className="flex-1 py-3 rounded-xl font-bold border-2 border-gray-200 text-gray-600 hover:bg-gray-50 transition"
+          >
+            Cancel
+          </button>
+          <button
+            onClick={onSave}
+            disabled={saving}
+            className="flex-1 py-3 rounded-xl font-bold bg-theme-primary text-white hover:bg-theme-primary/90 transition disabled:opacity-50 flex items-center justify-center gap-2"
+          >
+            {saving ? (
+              <>
+                <Loader2 size={20} className="animate-spin" />
+                Saving...
+              </>
+            ) : (
+              'Save Defaults'
+            )}
+          </button>
+        </div>
+      </motion.div>
+    </motion.div>
+  );
+};