backend: prescription start/end dates + dispense ledger

Add optional startDate/endDate columns to prescriptions (schema,
validation, types, service) — when set, endDate drives expiry.

Add a new append-only `dispenses` resource (schema, types, validation,
service, route at /api/dispenses) recording who received which medication,
gated on the existing inventory RBAC statement. Migration 0020.

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

backend/drizzle/0020_freezing_tomas.sql

@@ -0,0 +1,23 @@
+CREATE TABLE "dispenses" (
+	"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 DEFAULT '' NOT NULL,
+	"medication" text NOT NULL,
+	"dose" text DEFAULT '' NOT NULL,
+	"quantity" integer DEFAULT 0 NOT NULL,
+	"unit" text DEFAULT '' NOT NULL,
+	"prescription_id" uuid,
+	"dispensed_by" text,
+	"dispensed_by_name" text DEFAULT '' NOT NULL,
+	"dispensed_at" timestamp DEFAULT now() NOT NULL,
+	"notes" text,
+	"created_at" timestamp DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+ALTER TABLE "prescriptions" ADD COLUMN "start_date" date;--> statement-breakpoint
+ALTER TABLE "prescriptions" ADD COLUMN "end_date" date;--> statement-breakpoint
+ALTER TABLE "dispenses" ADD CONSTRAINT "dispenses_organization_id_organization_id_fk" FOREIGN KEY ("organization_id") REFERENCES "public"."organization"("id") ON DELETE cascade ON UPDATE no action;--> statement-breakpoint
+ALTER TABLE "dispenses" ADD CONSTRAINT "dispenses_dispensed_by_user_id_fk" FOREIGN KEY ("dispensed_by") REFERENCES "public"."user"("id") ON DELETE set null ON UPDATE no action;--> statement-breakpoint
+CREATE INDEX "dispenses_org_idx" ON "dispenses" USING btree ("organization_id");

backend/drizzle/meta/_journal.json

@@ -141,6 +141,13 @@
       "when": 1781538797034,
       "tag": "0019_black_mole_man",
       "breakpoints": true
+    },
+    {
+      "idx": 20,
+      "version": "7",
+      "when": 1781629630102,
+      "tag": "0020_freezing_tomas",
+      "breakpoints": true
     }
   ]
 }