feat: add typescript monorepo with pnpm workspaces and prisma database package

- root package.json + pnpm-workspace.yaml + tsconfig.base.json
- packages/types: canonical enums (TenantStatus, AgentState)
- packages/shared: re-exports types, base for future utilities
- packages/database: Prisma 7 schema with driver adapter (pg), initial
  tenants table matching agente.md section 29, first migration applied

packages/database/src/index.ts

@@ -0,0 +1,14 @@
+import { PrismaClient } from "@prisma/client";
+import { PrismaPg } from "@prisma/adapter-pg";
+
+export * from "@prisma/client";
+
+let prisma: PrismaClient | undefined;
+
+export function getPrismaClient(): PrismaClient {
+  if (!prisma) {
+    const adapter = new PrismaPg({ connectionString: process.env.DATABASE_URL });
+    prisma = new PrismaClient({ adapter });
+  }
+  return prisma;
+}