feat: replace screen state machine with React Router v7 URL routing

- Install react-router-dom
- Add slugify utility with full TDD test suite (7 tests)
- Wrap app in BrowserRouter in main.tsx
- Add optional onNavigate prop to ExamRunner.goTo
- Create ExamRoute component (deep-link restore + back/forward sync)
- Migrate App.tsx: replace screen useState with <Routes>, all setScreen()
  calls replaced with navigate(), add activateExam for deep-link activation,
  use useLocation for verify/reset-password special layouts
- Remove unused AppScreen type from types.ts

frontend/src/types.ts

@@ -1,125 +1,124 @@
 // src/types.ts
 
 export type QuestionType =
-  | 'multiple-choice'
-  | 'multiple-select'
-  | 'short-answer'
-  | 'translation'
-  | 'math-input'
-  | 'essay'
-  | 'match'
-  | 'order'
+  | "multiple-choice"
+  | "multiple-select"
+  | "short-answer"
+  | "translation"
+  | "math-input"
+  | "essay"
+  | "match"
+  | "order";
 
 export interface Choice {
-  id: string
-  text: string
+  id: string;
+  text: string;
 }
 
 export interface MatchItem {
-  id: string
-  text: string
+  id: string;
+  text: string;
 }
 
 export interface QuestionImage {
-  src: string
-  alt?: string
-  caption?: string
+  src: string;
+  alt?: string;
+  caption?: string;
 }
 
 export interface QuestionAudio {
-  src: string
+  src: string;
 }
 
 export interface QuestionCode {
-  language: string
-  content: string
+  language: string;
+  content: string;
 }
 
 export interface QuestionTable {
-  headers: string[]
-  rows: string[][]
+  headers: string[];
+  rows: string[][];
 }
 
 export interface Question {
-  id: string
-  type: QuestionType
-  category?: string
-  points?: number
-  prompt: string
-  explanation?: string
-  image?: QuestionImage
-  audio?: QuestionAudio
-  code?: QuestionCode
-  table?: QuestionTable
-  svg?: string
-  answer?: string | string[] | Record<string, string>
-  acceptedForms?: string[]
-  caseSensitive?: boolean
-  ignorePunctuation?: boolean
-  ignoreAccents?: boolean
-  sourceLanguage?: string
-  targetLanguage?: string
-  choices?: Choice[]
-  minWords?: number
-  rubric?: string[]
-  left?: MatchItem[]
-  right?: MatchItem[]
-  items?: MatchItem[]
+  id: string;
+  type: QuestionType;
+  category?: string;
+  points?: number;
+  prompt: string;
+  explanation?: string;
+  image?: QuestionImage;
+  audio?: QuestionAudio;
+  code?: QuestionCode;
+  table?: QuestionTable;
+  svg?: string;
+  answer?: string | string[] | Record<string, string>;
+  acceptedForms?: string[];
+  caseSensitive?: boolean;
+  ignorePunctuation?: boolean;
+  ignoreAccents?: boolean;
+  sourceLanguage?: string;
+  targetLanguage?: string;
+  choices?: Choice[];
+  minWords?: number;
+  rubric?: string[];
+  left?: MatchItem[];
+  right?: MatchItem[];
+  items?: MatchItem[];
 }
 
 export interface Exam {
-  title: string
-  subtitle?: string
-  author?: string
-  timeLimitMinutes?: number | null
-  feedbackMode?: 'end' | 'immediate'
-  passingScore?: number
-  categories?: string[]
-  questions: Question[]
+  title: string;
+  subtitle?: string;
+  author?: string;
+  timeLimitMinutes?: number | null;
+  feedbackMode?: "end" | "immediate";
+  passingScore?: number;
+  categories?: string[];
+  questions: Question[];
 }
 
-export type FeedbackMode = 'immediate' | 'end'
+export type FeedbackMode = "immediate" | "end";
 
 export interface ExamState {
-  currentIdx: number
-  answers: Record<string, unknown>
-  flags: Record<string, boolean>
-  notes: string
-  revealed?: Record<string, boolean>
-  startedAt: number
-  completedAt?: number
-  feedbackMode: FeedbackMode
+  currentIdx: number;
+  answers: Record<string, unknown>;
+  flags: Record<string, boolean>;
+  notes: string;
+  revealed?: Record<string, boolean>;
+  startedAt: number;
+  completedAt?: number;
+  feedbackMode: FeedbackMode;
 }
 
 export interface HistoryEntry {
-  id: string
-  title: string
-  completedAt: number
-  elapsedMs: number
-  gradedCount: number
-  correctCount: number
-  totalPoints: number
-  scorePoints: number
-  passingScore: number
-  exam: Exam
-  state: ExamState
+  id: string;
+  title: string;
+  completedAt: number;
+  elapsedMs: number;
+  gradedCount: number;
+  correctCount: number;
+  totalPoints: number;
+  scorePoints: number;
+  passingScore: number;
+  exam: Exam;
+  state: ExamState;
 }
 
-export type GradeStatus = 'correct' | 'wrong' | 'ungraded' | 'unanswered'
+export type GradeStatus = "correct" | "wrong" | "ungraded" | "unanswered";
 
 export interface GradeResult {
-  status: GradeStatus
-  correct: boolean
-  points: number
+  status: GradeStatus;
+  correct: boolean;
+  points: number;
 }
 
-export type AppScreen = 'landing' | 'exam' | 'results' | 'review' | 'verify' | 'reset-password' | 'admin'
-export type ThemeMode = 'light' | 'dark'
-export type FontSize = 'small' | 'medium' | 'large'
-export type FeedbackTweak = 'auto' | 'immediate' | 'end'
+export type ThemeMode = "light" | "dark";
+export type FontSize = "small" | "medium" | "large";
+export type FeedbackTweak = "auto" | "immediate" | "end";
 
 export interface Tweaks {
-  theme: ThemeMode
-  fontSize: FontSize
-  feedbackMode: FeedbackTweak
+  theme: ThemeMode;
+  fontSize: FontSize;
+  feedbackMode: FeedbackTweak;
 }