feat(01-03): Prisma tenant middleware, PostgreSQL RLS, and isolation tests

- Create src/lib/prisma-tenant.ts:
  - withTenantContext(tenantId) / createTenantPrisma — Prisma $extends client
  - Intercepts findMany, findFirst, findUnique, create, createMany, update,
    updateMany, delete, deleteMany, upsert, count, aggregate, groupBy on User
  - Auto-injects tenantId filter on all reads, writes, and deletes
  - setTenantRLS() helper for explicit RLS enforcement in transactions
  - TENANT_SCOPED_MODELS constant for future extensibility
- Create prisma/migrations/20260304104214_initial_schema — baseline migration
  capturing schema created by initial db push
- Create prisma/migrations/20260304104245_add_rls_policies:
  - ALTER TABLE User ENABLE ROW LEVEL SECURITY
  - CREATE POLICY tenant_isolation_user USING app.current_tenant_id session var
  - Defense-in-depth architecture comments explaining primary vs secondary enforcement
- Create src/lib/__tests__/tenant-isolation.test.ts (6 tests, all passing):
  - Test 1: Tenant A context returns only Tenant A's users (zero from B)
  - Test 2: Tenant B context returns only Tenant B's users (zero from A)
  - Test 3: create() auto-sets tenantId, invisible to other tenant
  - Test 4: findUnique by Tenant B's ID under Tenant A context returns null
  - Additional: findFirst cross-tenant blocked, count() is tenant-scoped

prisma/migrations/20260304104214_initial_schema/migration.sql

@@ -0,0 +1,60 @@
+-- =============================================================================
+-- Initial Schema Migration
+-- Created as a baseline to capture the state created by `prisma db push`
+-- during project initialization (01-01-PLAN.md).
+--
+-- This migration is marked as applied without running it (baseline approach)
+-- since the schema already exists in the database from the initial db push.
+-- =============================================================================
+
+-- CreateEnum
+CREATE TYPE "TenantStatus" AS ENUM ('ACTIVE', 'PENDING_SUSPENSION', 'SUSPENDED');
+
+-- CreateEnum
+CREATE TYPE "Role" AS ENUM ('ADMIN', 'OFFICE_STAFF', 'COLLECTOR', 'TECHNICIAN', 'CLIENT');
+
+-- CreateTable
+CREATE TABLE "Tenant" (
+    "id" TEXT NOT NULL,
+    "name" TEXT NOT NULL,
+    "slug" TEXT NOT NULL,
+    "ownerEmail" TEXT NOT NULL,
+    "businessAddress" TEXT,
+    "contactPhone" TEXT,
+    "status" "TenantStatus" NOT NULL DEFAULT 'ACTIVE',
+    "suspendedAt" TIMESTAMP(3),
+    "gracePeriodEndsAt" TIMESTAMP(3),
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "Tenant_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "User" (
+    "id" TEXT NOT NULL,
+    "email" TEXT NOT NULL,
+    "passwordHash" TEXT NOT NULL,
+    "firstName" TEXT NOT NULL,
+    "lastName" TEXT NOT NULL,
+    "tenantId" TEXT,
+    "roles" "Role"[],
+    "isActive" BOOLEAN NOT NULL DEFAULT true,
+    "isSuperAdmin" BOOLEAN NOT NULL DEFAULT false,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "User_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "Tenant_slug_key" ON "Tenant"("slug");
+
+-- CreateIndex
+CREATE INDEX "User_tenantId_idx" ON "User"("tenantId");
+
+-- CreateIndex
+CREATE UNIQUE INDEX "User_email_tenantId_key" ON "User"("email", "tenantId");
+
+-- AddForeignKey
+ALTER TABLE "User" ADD CONSTRAINT "User_tenantId_fkey" FOREIGN KEY ("tenantId") REFERENCES "Tenant"("id") ON DELETE CASCADE ON UPDATE CASCADE;