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/shared/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "@b2bcall/shared",
+  "version": "0.0.1",
+  "private": true,
+  "main": "src/index.ts",
+  "types": "src/index.ts",
+  "scripts": {
+    "typecheck": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@b2bcall/types": "workspace:*"
+  },
+  "devDependencies": {
+    "typescript": "^5.7.0"
+  }
+}

packages/shared/src/index.ts

@@ -0,0 +1 @@
+export * from "@b2bcall/types";

packages/shared/tsconfig.json

@@ -0,0 +1,8 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "dist",
+    "rootDir": "src"
+  },
+  "include": ["src"]
+}