Add exclude from budget tracking option per account

Accounts (e.g. mortgage) can be toggled to exclude from budget tracking:
- Their transactions don't reduce envelope spending
- Their balance is excluded from Available to Budget
- Account card shows "excluded from budget" badge when enabled

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/page.tsx

@@ -30,6 +30,7 @@ interface Account {
   accountNumber?: string;
   color: string;
   isActive: boolean;
+  excludeFromBudget?: boolean;
   defaultPaycheckAmount?: number;
 }
 
@@ -144,13 +145,15 @@ export default function BudgetDashboard() {
 
   // ── Derived helpers ──────────────────────────────────────────────────────────
 
-  const calculateEnvelopeSpending = useCallback((envs: Envelope[], txns: Transaction[]): Envelope[] =>
+  const calculateEnvelopeSpending = useCallback((envs: Envelope[], txns: Transaction[], accs?: Account[]): Envelope[] => {
-    envs.map(envelope => {
+    const excludedIds = new Set((accs ?? accounts).filter(a => a.excludeFromBudget).map(a => a.id));
+    return envs.map(envelope => {
       const spent = txns
-        .filter(t => t.envelopeId === envelope.id && t.amount < 0)
+        .filter(t => t.envelopeId === envelope.id && t.amount < 0 && !excludedIds.has(t.accountId))
         .reduce((sum, t) => sum + Math.abs(t.amount), 0);
       return { ...envelope, spent };
-    }), []);
+    });
+  }, [accounts]);
 
   const calculateAccountBalances = useCallback((accs: Account[], txns: Transaction[]): Account[] => {
     const map = new Map<string, number>();
@@ -929,10 +932,10 @@ export default function BudgetDashboard() {
       return e.allocated + incomeAlloc > 0 && e.spent > e.allocated + incomeAlloc;
     });
 
-    // Available to budget = all asset accounts minus total envelope allocations
+    // Available to budget = all asset accounts (excluding budget-excluded ones) minus total envelope allocations
     const LIABILITY_TYPES = ['credit_card', 'mortgage', 'loan'];
     const liquidBalance = accounts
-      .filter(a => !LIABILITY_TYPES.includes(a.type))
+      .filter(a => !LIABILITY_TYPES.includes(a.type) && !a.excludeFromBudget)
       .reduce((s, a) => s + a.balance, 0);
     const totalAllocated = envelopes.reduce((s, e) => s + e.allocated, 0);
     const availableToBudget = liquidBalance - totalAllocated;

src/components/AccountManagement.tsx

@@ -12,6 +12,7 @@ interface Account {
   accountNumber?: string;
   color: string;
   isActive: boolean;
+  excludeFromBudget?: boolean;
 }
 
 interface AccountManagementProps {
@@ -187,6 +188,9 @@ export default function AccountManagement({ accounts, onAccountAdd, onAccountUpd
                     <p className={`text-sm ${account.isActive ? 'text-green-600' : 'text-gray-500'}`}>
                       {account.isActive ? 'Active' : 'Inactive'}
                     </p>
+                    {account.excludeFromBudget && (
+                      <span className="text-xs bg-gray-100 text-gray-500 px-1.5 py-0.5 rounded">excluded from budget</span>
+                    )}
                   </div>
 
                   <div className="flex space-x-2">
@@ -316,6 +320,20 @@ export default function AccountManagement({ accounts, onAccountAdd, onAccountUpd
                 <label htmlFor="isActive" className="text-sm text-gray-700">Active Account</label>
               </div>
 
+              <div className="flex items-start gap-2">
+                <input
+                  type="checkbox"
+                  id="excludeFromBudget"
+                  checked={formData.excludeFromBudget ?? false}
+                  onChange={(e) => setFormData(prev => ({ ...prev, excludeFromBudget: e.target.checked }))}
+                  className="mr-2 mt-0.5"
+                />
+                <label htmlFor="excludeFromBudget" className="text-sm text-gray-700">
+                  Exclude from budget tracking
+                  <span className="block text-xs text-gray-400">Transactions on this account won't count against envelopes or expenses (e.g. mortgage payments)</span>
+                </label>
+              </div>
+
               <div className="flex justify-end space-x-3 pt-4">
                 <button
                   type="button"