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/types/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "@b2bcall/types",
+  "version": "0.0.1",
+  "private": true,
+  "main": "src/index.ts",
+  "types": "src/index.ts",
+  "scripts": {
+    "typecheck": "tsc --noEmit"
+  },
+  "devDependencies": {
+    "typescript": "^5.7.0"
+  }
+}