fix(seed): use tsconfig.app.json instead of inline --compiler-options (#235)

## Summary

Follow-up to [#234](#234). The `db:seed` script's inline `--compiler-options '{"module":"CommonJS",…}'` was getting its quotes stripped by the shell when `pnpm run` re-spawned `ts-node`:

```
> ts-node --compiler-options {module:CommonJS,esModuleInterop:true,target:ES2020} apps/portal-bff/prisma/seed.ts

SyntaxError: Expected property name or '}' in JSON at position 1
```

Cross-platform JSON-on-cmdline quoting through nested `package.json → shell → npm-script → shell → ts-node` is a notorious pain. `apps/portal-bff/tsconfig.app.json` already declares everything `ts-node` needs to transpile the seed (module=commonjs, esModuleInterop=true, target=es2021, moduleResolution=node, types=[node]). Point at it with `-P` and drop the inline JSON entirely.

## What lands

| File | Change |
| --- | --- |
| `package.json` (root) | `db:seed` script: `--compiler-options '{...}'` → `-P apps/portal-bff/tsconfig.app.json`. One-line diff. |

That's it.

## Why `tsconfig.app.json` works for the seed even though seed.ts isn't under `src/`

`ts-node --transpile-only` reads `compilerOptions` from the `-P` tsconfig but **ignores the `include` / `exclude` fields** for the file passed explicitly on the command line. So the fact that `tsconfig.app.json` has `"include": ["src/**/*.ts"]` and the seed lives under `prisma/` doesn't matter — `ts-node` happily transpiles whatever file you point it at.

## Test plan

- [ ] **Locally**: `cd apps/portal-bff && pnpm exec prisma db seed` — no more `SyntaxError` on the compiler-options, seed runs and reports `[seed] test-tenant complete …`.
- [ ] **Idempotency** — re-run, expect `created 0 / 0 / 0`.
- [x] No application code changed — drift gate / lint / tests untouched.

## Notes for the reviewer

- Could have created a dedicated `apps/portal-bff/prisma/tsconfig.json` extending the app config. Less coupling but more files; pointing at the existing `tsconfig.app.json` is the minimum-surface fix.
- The Prisma 7 deprecation warning about `package.json#prisma` is unchanged; migrating to `prisma.config.ts` is a separate future PR (would also let us inline the seed config without shell quoting at all).

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #235

package.json

@@ -17,7 +17,7 @@
     "docs:dev": "vitepress dev docs",
     "docs:build": "vitepress build docs",
     "docs:preview": "vitepress preview docs",
-    "db:seed": "ts-node --transpile-only --compiler-options {\"module\":\"CommonJS\",\"esModuleInterop\":true,\"target\":\"ES2020\"} apps/portal-bff/prisma/seed.ts"
+    "db:seed": "ts-node --transpile-only -P apps/portal-bff/tsconfig.app.json apps/portal-bff/prisma/seed.ts"
   },
   "private": true,
   "lint-staged": {