Refactor: Use backend API for inventory sync (matches web app)

PROBLEM:
- Content script trying to fetch from Steam directly
- Getting HTML instead of JSON (privacy/auth issues)
- Complex error-prone approach

SOLUTION:
- Extension calls backend API (same as web app)
- Backend fetches from Steam (server-side Steam API)
- Backend enriches with prices and float values
- Backend stores in database
- Returns stats to extension

FLOW:
1. User clicks "Sync Full Inventory" button
2. Popup → Background → POST /api/steam/inventory/sync
3. Backend (Investment API):
   - Fetches Steam inventory
   - Converts to JSON
   - Enriches with market prices
   - Stores in portfolio table
4. Returns: {success, added, updated, skipped, total}

BENEFITS:
- No Steam cookie/auth issues
- Automatic price enrichment
- Automatic float value lookup
- Consistent with web app
- More reliable

Based on API docs: D:\AppADay\cs2float-checker\csfloat-api-docs\pages\steam-integration.mdx

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: rainerstudios

popup.js

@@ -510,90 +510,50 @@ async function syncTransactionsFromPopup() {
  */
 /**
  * Sync inventory from popup
- * Opens Steam inventory page and triggers content script sync
- * MUST use content script to bypass Steam's 10-day restriction
+ * Calls backend API (same as web app "Import from Steam")
+ * Backend fetches from Steam, enriches with prices, stores in DB
  */
 async function syncInventoryFromPopup() {
   const button = document.getElementById('syncInventoryBtn');
   const originalText = button.innerHTML;
 
   try {
-    button.innerHTML = '⏳ Opening Inventory...';
+    button.innerHTML = '📦 Syncing...';
     button.disabled = true;
 
-    console.log('[Popup] Opening Steam inventory page...');
+    console.log('[Popup] Calling backend inventory sync API...');
 
-    // Step 1: Open or focus Steam inventory tab
-    let tabs = await chrome.tabs.query({ url: 'https://steamcommunity.com/*/inventory*' });
-
-    let tab;
-    if (tabs.length > 0) {
-      tab = tabs[0];
-      await chrome.tabs.update(tab.id, { active: true });
-      console.log('[Popup] Found existing inventory tab:', tab.id);
-    } else {
-      tab = await chrome.tabs.create({
-        url: 'https://steamcommunity.com/my/inventory',
-        active: true
-      });
-      console.log('[Popup] Created new inventory tab:', tab.id);
-
-      // Wait for page to load (longer wait for new tab)
-      await new Promise(resolve => setTimeout(resolve, 4000));
-    }
-
-    button.innerHTML = '📦 Syncing Inventory...';
-
-    // Step 2: Try to send message with retry logic
-    const maxRetries = 5;
-    let lastError = null;
-
-    for (let attempt = 1; attempt <= maxRetries; attempt++) {
-      try {
-        console.log(`[Popup] Attempt ${attempt}/${maxRetries} to contact content script...`);
-
-        const response = await chrome.tabs.sendMessage(tab.id, {
-          type: 'CS2_SYNC_INVENTORY'
-        });
-
-        if (response && response.success) {
-          console.log('[Popup] ✅ Sync successful:', response);
+    // Call backend API via background script
+    const response = await chrome.runtime.sendMessage({
+      type: 'SYNC_INVENTORY_API'
+    });
 
-          button.innerHTML = `✅ Synced ${response.itemCount || 0} Items!`;
-          button.style.background = 'linear-gradient(135deg, #22c55e, #16a34a)';
+    if (response && response.success) {
+      console.log('[Popup] ✅ Sync successful:', response);
 
-          setTimeout(() => {
-            button.innerHTML = originalText;
-            button.style.background = '';
-            button.disabled = false;
-          }, 3000);
+      const stats = response.stats || {};
+      const total = stats.added || 0 + stats.updated || 0;
 
-          return; // Success!
-        } else {
-          throw new Error(response?.error || 'Failed to sync inventory');
-        }
+      button.innerHTML = `✅ Synced ${total} Items!`;
+      button.style.background = 'linear-gradient(135deg, #22c55e, #16a34a)';
 
-      } catch (error) {
-        lastError = error;
-        console.warn(`[Popup] Attempt ${attempt} failed:`, error.message);
+      setTimeout(() => {
+        button.innerHTML = originalText;
+        button.style.background = '';
+        button.disabled = false;
+      }, 3000);
 
-        if (attempt < maxRetries) {
-          // Wait before retry (exponential backoff)
-          await new Promise(resolve => setTimeout(resolve, 1000 * attempt));
-        }
-      }
+    } else {
+      throw new Error(response?.error || 'Failed to sync inventory');
     }
 
-    // All retries failed
-    throw lastError || new Error('Failed to contact content script');
-
   } catch (error) {
     console.error('[Popup] ❌ Inventory sync failed:', error);
 
     button.innerHTML = '❌ Sync Failed';
     button.style.background = 'linear-gradient(135deg, #ef4444, #dc2626)';
 
-    alert(`Failed to sync inventory:\n${error.message}\n\nTroubleshooting:\n1. Make sure you're logged into Steam\n2. Reload the extension (chrome://extensions)\n3. Try again from your inventory page`);
+    alert(`Failed to sync inventory:\n${error.message}\n\nMake sure:\n1. You're logged into SteamLedger\n2. Your Steam account is linked\n3. Your Steam inventory is set to Public`);
 
     setTimeout(() => {
       button.innerHTML = originalText;