feat: add fullscreen mode and extract shared game engine

- Add new fullscreen game mode playable in a dedicated browser tab
- Extract shared game logic into `engine.js` to be used by both popup and fullscreen modes
- Implement self-protection to prevent closing the game tab or popup tab
- Update documentation and bump version to 1.1.0

game.js

@@ -0,0 +1,127 @@
+/* ============================================================
+   TAB SHOOTER — Vollbild-Controller (game.html)
+   Läuft als eigener Tab. Dieser Tab wird über seine ID
+   von der Zielliste ausgeschlossen -> er lässt sich NICHT abschießen.
+   ============================================================ */
+
+import { TabShooterGame, loadTabs } from "./engine.js";
+
+// ---------- DOM ----------
+const canvas = document.getElementById("game-canvas");
+const screens = {
+  start: document.getElementById("start-screen"),
+  game: document.getElementById("game-screen"),
+  gameover: document.getElementById("gameover-screen"),
+  empty: document.getElementById("empty-screen"),
+};
+const els = {
+  hsValue: document.getElementById("hs-value"),
+  hudScore: document.getElementById("hud-score"),
+  hudLives: document.getElementById("hud-lives"),
+  hudTabs: document.getElementById("hud-tabs"),
+  hudPowerups: document.getElementById("hud-powerups"),
+  resultTabs: document.getElementById("result-tabs"),
+  resultScore: document.getElementById("result-score"),
+  resultHighscore: document.getElementById("result-highscore"),
+  newRecord: document.getElementById("new-record"),
+};
+
+// ---------- STATE ----------
+let game = null;
+let highscore = 0;
+let selectedScope = "current";
+let myTabId = null;
+
+// Eigene Tab-ID herausfinden – damit wir sie aus der Zielliste streichen können.
+(async () => {
+  try {
+    const [tab] = await chrome.tabs.getCurrent();
+    if (tab) myTabId = tab.id;
+  } catch (_) {
+    // getCurrent() schlägt fehlt, wenn wir gar kein Tab sind (sollte nicht passieren)
+  }
+})();
+
+// ---------- SCREEN HELPERS ----------
+function showScreen(name) {
+  Object.values(screens).forEach((s) => s.classList.remove("visible"));
+  screens[name].classList.add("visible");
+}
+
+// ---------- HIGHSCORE ----------
+async function loadHighscore() {
+  const data = await chrome.storage.local.get("highscore");
+  highscore = data.highscore || 0;
+  els.hsValue.textContent = highscore;
+}
+async function saveHighscore(value) {
+  await chrome.storage.local.set({ highscore: value });
+  highscore = value;
+}
+
+// ---------- HUD CALLBACKS ----------
+const hudCallbacks = {
+  onScore: (s) => (els.hudScore.textContent = s),
+  onLives: (l) => (els.hudLives.textContent = "❤️".repeat(Math.max(0, l))),
+  onTabs: (t) => (els.hudTabs.textContent = t),
+  onPowerups: (g) => {
+    let html = "";
+    if (g.shield > 0) html += "🛡️";
+    if (g.tripleShot > 0) html += "🔫";
+    if (g.rapidFire > 0) html += "⚡";
+    els.hudPowerups.innerHTML = html;
+  },
+  onGameOver: ({ score }) => {
+    const isNewRecord = score > highscore;
+    if (isNewRecord) saveHighscore(score);
+    els.resultTabs.textContent = game.tabsDestroyed;
+    els.resultScore.textContent = score;
+    els.resultHighscore.textContent = Math.max(highscore, score);
+    els.newRecord.classList.toggle("hidden", !isNewRecord);
+    showScreen("gameover");
+  },
+};
+
+// ---------- GAME START ----------
+async function startNewGame() {
+  // WICHTIG: myTabId wird ausgeschlossen, damit dieser Tab kein Ziel ist.
+  const tabs = await loadTabs(selectedScope, myTabId);
+  if (tabs.length === 0) {
+    showScreen("empty");
+    return;
+  }
+  showScreen("game");
+  els.hudScore.textContent = "0";
+  els.hudLives.textContent = "❤️❤️❤️";
+  els.hudTabs.textContent = tabs.length;
+  els.hudPowerups.innerHTML = "";
+
+  game = new TabShooterGame(canvas, {}, hudCallbacks);
+  await game.init(tabs);
+  game.start();
+}
+
+// ---------- EVENT WIRING ----------
+document.querySelectorAll(".scope-btn").forEach((btn) => {
+  btn.addEventListener("click", () => {
+    document.querySelectorAll(".scope-btn").forEach((b) => b.classList.remove("active"));
+    btn.classList.add("active");
+    selectedScope = btn.dataset.scope;
+  });
+});
+
+document.getElementById("start-btn").addEventListener("click", startNewGame);
+document.getElementById("replay-btn").addEventListener("click", startNewGame);
+
+document.getElementById("menu-btn").addEventListener("click", () => {
+  if (game) game.stop();
+  loadHighscore();
+  showScreen("start");
+});
+document.getElementById("empty-menu-btn").addEventListener("click", () => {
+  loadHighscore();
+  showScreen("start");
+});
+
+// ---------- INIT ----------
+loadHighscore();