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

package.json

@@ -0,0 +1,19 @@
+{
+  "name": "b2bcall",
+  "private": true,
+  "version": "0.0.1",
+  "packageManager": "pnpm@11.24.0",
+  "engines": {
+    "node": ">=22"
+  },
+  "scripts": {
+    "build": "pnpm -r --if-present run build",
+    "dev": "pnpm -r --if-present --parallel run dev",
+    "lint": "pnpm -r --if-present run lint",
+    "typecheck": "pnpm -r --if-present run typecheck",
+    "test": "pnpm -r --if-present run test"
+  },
+  "devDependencies": {
+    "typescript": "^5.9.3"
+  }
+}