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/drizzle/0015_polite_captain_marvel.sql

@@ -0,0 +1,23 @@
+CREATE TABLE "invoices" (
+	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+	"organization_id" text NOT NULL,
+	"patient_file_number" text DEFAULT '' NOT NULL,
+	"patient_name" text NOT NULL,
+	"patient_initials" text NOT NULL,
+	"number" text NOT NULL,
+	"issued_at" date DEFAULT now() NOT NULL,
+	"due_at" date,
+	"status" text NOT NULL,
+	"line_items" jsonb NOT NULL,
+	"installments" jsonb NOT NULL,
+	"notes" text,
+	"source" text DEFAULT 'manual' NOT NULL,
+	"created_by" text,
+	"created_at" timestamp DEFAULT now() NOT NULL,
+	"updated_at" timestamp DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+ALTER TABLE "invoices" ADD CONSTRAINT "invoices_organization_id_organization_id_fk" FOREIGN KEY ("organization_id") REFERENCES "public"."organization"("id") ON DELETE cascade ON UPDATE no action;--> statement-breakpoint
+ALTER TABLE "invoices" ADD CONSTRAINT "invoices_created_by_user_id_fk" FOREIGN KEY ("created_by") REFERENCES "public"."user"("id") ON DELETE set null ON UPDATE no action;--> statement-breakpoint
+CREATE INDEX "invoices_org_idx" ON "invoices" USING btree ("organization_id");--> statement-breakpoint
+CREATE INDEX "invoices_org_file_idx" ON "invoices" USING btree ("organization_id","patient_file_number");

backend/drizzle/meta/_journal.json

@@ -106,6 +106,13 @@
       "when": 1781454115877,
       "tag": "0014_youthful_aqueduct",
       "breakpoints": true
+    },
+    {
+      "idx": 15,
+      "version": "7",
+      "when": 1781455848772,
+      "tag": "0015_polite_captain_marvel",
+      "breakpoints": true
     }
   ]
 }