Initial release: PokeRogue Type Effectiveness extension

Chrome/Firefox MV3 extension that shows move type effectiveness during
PokeRogue battles. Features:

- Auto-detects battle state via Phaser game bridge (MAIN world)
- Shows effectiveness multiplier, base power, and physical/special category
- Supports single and double battles
- Manual type calculator mode as fallback
- Draggable overlay with dark theme matching PokeRogue aesthetic
- Settings popup with position, opacity, and display options
- Complete Gen 6+ type chart (18 types) from PokeRogue source data
- Type colors matching PokeRogue's own color scheme

service-worker.js

@@ -0,0 +1,40 @@
+/**
+ * PokeRogue Type Effectiveness - Service Worker (Background)
+ *
+ * Handles extension lifecycle events and message routing.
+ */
+
+// Default settings applied on install
+const DEFAULT_SETTINGS = {
+  enabled: true,
+  position: 'top-right',
+  opacity: 90,
+  showPower: true,
+  showCategory: true,
+  showMoveNames: true,
+  compactMode: false,
+  manualMode: false,
+  manualEnemyTypes: []
+};
+
+// On install, set default settings
+chrome.runtime.onInstalled.addListener((details) => {
+  if (details.reason === 'install') {
+    chrome.storage.local.set({ settings: DEFAULT_SETTINGS });
+    console.log('[PokeRogue Ext] Installed with default settings');
+  }
+});
+
+// Handle messages from popup or content scripts
+chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
+  if (message.type === 'GET_SETTINGS') {
+    chrome.storage.local.get(['settings'], (result) => {
+      sendResponse(result.settings || DEFAULT_SETTINGS);
+    });
+    return true; // async response
+  }
+
+  if (message.type === 'PING') {
+    sendResponse({ pong: true, version: '1.0.0' });
+  }
+});