Refactor: Centralize Prisma schema and restrict DB access

This commit refactors the project to use a shared Prisma schema and restricts direct database access to the API service.

Key changes:

- Created a new shared package `core/prisma` containing the Prisma schema, generated client, and types.
- Configured the monorepo to use NPM workspaces, including `core/prisma` and all services.
- Updated all services (`api`, `ui`, `mcp`, `agent`, and the background processing service) to depend on `@empresa/prisma-schema`.
- The API service now imports `PrismaClient` from `@empresa/prisma-schema/client`.
- Other services import only types from `@empresa/prisma-schema`.
- Removed redundant Prisma configurations from `api` and the background processing service.
- Updated the background processing service's `sync-empleados.js` to fetch data via an API call instead of direct database access.
- Updated TypeScript configurations (`tsconfig.base.json` and service-specific ones) to support the new structure and path aliases.
- Updated `README.md` to reflect the new architecture and added convenience scripts for Prisma operations.

This change promotes a single source of truth for data models, reduces code duplication, and improves the overall architecture by centralizing database operations within the API service.

package.json

@@ -0,0 +1,18 @@
+{
+  "name": "empresa-monorepo",
+  "version": "1.0.0",
+  "private": true,
+  "workspaces": [
+    "agent",
+    "api",
+    "core/prisma",
+    "mcp",
+    "ui",
+    "worker"
+  ],
+  "scripts": {
+    "db:generate": "npm run db:generate --workspace=@empresa/prisma-schema",
+    "prisma:migrate:dev": "npm run prisma:migrate:dev --workspace=@empresa/prisma-schema",
+    "prisma:deploy": "npm run prisma:deploy --workspace=@empresa/prisma-schema"
+  }
+}