Add intro screen, win/loss art, and a way to abandon the ritual

- Adds a full-screen intro/title screen (new 'intro' game phase) with
  a moody Malmö/Turning Torso background and a "Börja ritualen"
  button; the game no longer starts ticking until the player begins.
- Win and loss overlays now show matching generated artwork behind
  the existing text, instead of a flat scrim.
- New "Avbryt" header button lets the player abandon a run mid-game
  (with a confirm prompt) via a new 'abandoned' phase, reusing the
  existing overlay/restart flow.
- Source images converted from PNG (~2.1MB each) to WebP (~120KB
  each) and placed under public/img/ so Vite serves them as-is.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/engine.ts

@@ -24,7 +24,7 @@ export interface State {
   areas: { rosengard: boolean; varnhem: boolean; torso: boolean };
   upgrades: Set<string>;
   log: LogEntry[];
-  phase: 'playing' | 'won' | 'lost';
+  phase: 'intro' | 'playing' | 'won' | 'lost' | 'abandoned';
   lostReason?: string;
   usedEventIds: Set<string>;
   flags: Set<string>;
@@ -69,7 +69,7 @@ export function createState(): State {
     areas: { rosengard: false, varnhem: false, torso: false },
     upgrades: new Set(),
     log: [{ tick: 0, text: 'Mötet började i en fuktig källare i Rosengård. Nio stolar. En av dem är alltid lite för varm.', kind: 'system' }],
-    phase: 'playing',
+    phase: 'intro',
     usedEventIds: new Set(),
     flags: new Set(),
     nextEventTick: EVENT_INTERVAL_TICKS,
@@ -78,6 +78,19 @@ export function createState(): State {
   };
 }
 
+export function startGame(state: State): State {
+  if (state.phase !== 'intro') return state;
+  return { ...state, phase: 'playing' };
+}
+
+export function abandonGame(state: State): State {
+  return {
+    ...state,
+    phase: 'abandoned',
+    log: [{ tick: state.tick, text: 'Ni lämnar källaren. Cirkeln bryts. Den Sovande sover vidare, ovetande, ofärdig.', kind: 'system' }, ...state.log],
+  };
+}
+
 function pickEvent(pool: GameEvent[], state: State): GameEvent | null {
   const available = pool.filter(e => {
     if (state.usedEventIds.has(e.id)) return false;