Fix alerts to read steamId from betterAuthUser like watchlist

REAL ROOT CAUSE:
- Watchlist reads: chrome.storage.local.get(['betterAuthUser']).steamId
- Alerts tried to read: g_steamID from page (always null on market pages)

FIX:
- Changed content.js to read from betterAuthUser.steamId
- Now matches watchlist implementation exactly (line 109-113)
- Uses the SAME auth data that watchlist uses

Console logs prove this:
- Watchlist: 'Found Steam ID from stored auth: 76561199094452064' ✅
- Alerts (before): 'Steam ID from page: null' ❌
- Alerts (after): Will read from betterAuthUser ✅

Author: rainerstudios

content.js

@@ -1727,12 +1727,19 @@ function showPriceAlertDialog(floatData) {
 async function setPriceAlert(itemName, targetPrice, alertType, maxFloat, floatData) {
   const alertKey = `alert_${itemName}_${Date.now()}`;
 
-  // Get Steam ID from page (same as watchlist does)
+  // Get Steam ID from stored auth (SAME as watchlist does - line 109-113 in watchlistButton.js)
   let steamId = null;
-  if (typeof g_steamID !== 'undefined' && g_steamID) {
-    steamId = g_steamID;
+  try {
+    const result = await chrome.storage.local.get(['betterAuthUser']);
+    if (result.betterAuthUser && result.betterAuthUser.steamId) {
+      steamId = result.betterAuthUser.steamId;
+      console.log('[Alert] Found Steam ID from stored auth:', steamId);
+    } else {
+      console.warn('[Alert] No Steam ID found in stored auth');
+    }
+  } catch (e) {
+    console.error('[Alert] Could not access extension storage:', e);
   }
-  console.log('[Alert] Steam ID from page:', steamId);
 
   try {
     // Wrap chrome.runtime.sendMessage in a try-catch to handle context invalidation