fix: bullet tax balance + expenses total (v1.4.5)

Three bugs:
1. weeklyExpenses total omitted bulletTax from the sum (both getData paths)
   Fix: add (_exp.bulletTax||0) to the calculation
2. _applyBulletTax read undefined credits as 0 (actors created before the
   credits field existed have null/undefined, not zero)
   Fix: fallback to 500 (template default) only when value is null/undefined
3. Finances tab CURRENT BALANCE showed just C because input had no placeholder
   Fix: add placeholder=500 min=0 to the credits input in character-sheet.hbs

templates/actor/character-sheet.hbs

@@ -873,7 +873,7 @@
 
 				<div class="finances-credits-hero">
 					<span class="fin-credit-label">CURRENT BALANCE</span>
-					<span class="fin-credit-value"><input type="number" name="system.details.credits" value="{{system.details.credits}}" /> c</span>
+					<span class="fin-credit-value"><input type="number" name="system.details.credits" value="{{system.details.credits}}" placeholder="500" min="0" /> c</span>
 					{{#if system.finances.debt}}<span class="fin-debt-badge">⚠ DEBT {{system.finances.debt}}c</span>{{/if}}
 				</div>