Rename Total Earnings to Total Balance, fix first-day delta

Total Balance reflects cumulative balance across all services.
Today/Month show real deltas from tracking start.
Baseline records inserted so first collection day shows zero delta.

Author: GeiserX

app/templates/dashboard.html

@@ -8,7 +8,7 @@
 <!-- Stats Row -->
 <div class="stats-grid">
   <div class="stat-card">
-    <div class="stat-label">Total Earnings</div>
+    <div class="stat-label">Total Balance</div>
     <div class="stat-value highlight" id="total-earnings">$0.00</div>
   </div>
   <div class="stat-card">