feat(treasury): show who still owes on the finance pages

Partial receipts and payments stay tied to a customer, company, or user, and the open balance is listed on the income and expense screens.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/src/treasury/treasury.controller.ts

@@ -92,6 +92,29 @@ export class TreasuryController {
     return this.treasury.transfer(user, body);
   }
 
+  @Get('parties')
+  parties(@CurrentUser() user: Actor, @Query('q') q?: string) {
+    return this.treasury.searchParties(user, q);
+  }
+
+  @Post('parties/person')
+  createPartyPerson(
+    @CurrentUser() user: Actor,
+    @Body() body: { firstName?: string; lastName?: string },
+  ) {
+    return this.treasury.createPartyPerson(user, body);
+  }
+
+  @Post('parties/company')
+  createPartyCompany(@CurrentUser() user: Actor, @Body() body: { name?: string }) {
+    return this.treasury.createPartyCompany(user, body);
+  }
+
+  @Get('party-balances')
+  partyBalances(@CurrentUser() user: Actor, @Query('kind') kind?: string) {
+    return this.treasury.partyBalances(user, kind === 'expense' ? 'expense' : 'income');
+  }
+
   @Get('documents')
   documents(
     @CurrentUser() user: Actor,