feat: invoices — patient billing with installments + PDF export

Backend (new `invoice` RBAC resource, granted to clinicians + reception):
- invoices table (line items + installments as JSONB), types, zod validation,
  service (CRUD + splitIntoInstallments + auto invoice numbers), org-scoped
  REST routes mounted at /api/invoices, activity logging (migration 0015)

Frontend:
- lib/invoices.ts API client + money/date helpers
- /invoices page: list with KPIs and search, create/edit dialog (searchable
  patient combobox, inline line-item editor, live total), detail sheet to split
  a bill into equal monthly installments, delete, and Download PDF
- dependency-free PDF via a print-styled window (browser "Save as PDF")
- sidebar "Invoices" entry under the Patients group; "Added by AI" badge honored

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/db/schema/index.ts

@@ -3,6 +3,7 @@ export * from "./patients.js";
 export * from "./notes.js";
 export * from "./appointments.js";
 export * from "./prescriptions.js";
+export * from "./invoices.js";
 export * from "./inventory.js";
 export * from "./tasks.js";
 export * from "./activity.js";

backend/src/db/schema/invoices.ts

@@ -0,0 +1,55 @@
+import {
+  date,
+  index,
+  jsonb,
+  pgTable,
+  text,
+  timestamp,
+  uuid,
+} from "drizzle-orm/pg-core";
+
+import type {
+  InvoiceInstallment,
+  InvoiceLineItem,
+  InvoiceStatus,
+} from "../../types/invoice.js";
+import { organization, user } from "./auth.js";
+
+// One row per patient invoice, scoped to a clinic (organization). Patient
+// identity is denormalized (name/initials/file number) so the ledger renders
+// without joining. Line items and installments are stored as JSONB. `issuedAt`
+// defaults to today.
+export const invoices = pgTable(
+  "invoices",
+  {
+    id: uuid("id").primaryKey().defaultRandom(),
+    organizationId: text("organization_id")
+      .notNull()
+      .references(() => organization.id, { onDelete: "cascade" }),
+    patientFileNumber: text("patient_file_number").notNull().default(""),
+    patientName: text("patient_name").notNull(),
+    patientInitials: text("patient_initials").notNull(),
+    number: text("number").notNull(),
+    issuedAt: date("issued_at").defaultNow().notNull(),
+    dueAt: date("due_at"),
+    status: text("status").$type<InvoiceStatus>().notNull(),
+    lineItems: jsonb("line_items").$type<InvoiceLineItem[]>().notNull(),
+    installments: jsonb("installments")
+      .$type<InvoiceInstallment[]>()
+      .notNull(),
+    notes: text("notes"),
+    source: text("source").$type<"manual" | "ai">().notNull().default("manual"),
+    createdBy: text("created_by").references(() => user.id, {
+      onDelete: "set null",
+    }),
+    createdAt: timestamp("created_at").defaultNow().notNull(),
+    updatedAt: timestamp("updated_at")
+      .defaultNow()
+      .$onUpdate(() => new Date())
+      .notNull(),
+  },
+  (t) => [
+    index("invoices_org_idx").on(t.organizationId),
+    index("invoices_org_file_idx").on(t.organizationId, t.patientFileNumber),
+  ],
+);