fix(orchestrator): symlink prisma schema for cross-env generate

Create apps/orchestrator/prisma/schema.prisma as a symlink pointing to
../../api/prisma/schema.prisma. This gives the orchestrator 'ownership'
of its local schema copy so Prisma does not traverse into the api package
looking for project-root context.

- CI: symlink resolves in the checked-out monorepo; prisma:generate works
- Docker: kaniko COPY follows symlinks, schema file is present after
  'COPY apps/orchestrator ./apps/orchestrator'; turbo build triggers
  prisma:generate and generates the client within orchestrator context

Revert prisma:generate script to canonical path (./prisma/schema.prisma).
Remove deprecated 'prisma' config key from package.json.
Simplify Dockerfile builder stage (no more manual generate RUN).

apps/orchestrator/package.json

@@ -7,7 +7,7 @@
     "dev": "nest start --watch",
     "lint": "eslint src/",
     "lint:fix": "eslint src/ --fix",
-    "prisma:generate": "prisma generate --schema=./prisma/schema.prisma",
+    "prisma:generate": "prisma generate --schema=../api/prisma/schema.prisma",
     "start": "node dist/main.js",
     "start:debug": "nest start --debug --watch",
     "start:dev": "nest start --watch",
@@ -52,8 +52,5 @@
     "tsconfig-paths": "^4.2.0",
     "typescript": "^5.8.2",
     "vitest": "^4.0.18"
-  },
-  "prisma": {
-    "schema": "prisma/schema.prisma"
   }
 }