fix(ci): declare packageManager for pnpm/action-setup (#6)

## Summary

- Add `"packageManager": "pnpm@10.33.2"` to root `package.json`.

## Motivation

The smoke-test CI run got past `actions/checkout@v4` (runner image fix from PR #4 working), but failed on `pnpm/action-setup@v3` with:

```
Error: No pnpm version is specified.
Please specify it by one of the following ways:
  - in the GitHub Action config with the key "version"
  - in the package.json with the key "packageManager"
```

The action looks at `package.json`'s `packageManager` field by default. Setting it there (rather than hardcoding `version:` in every workflow YAML) is the single-source-of-truth approach: corepack reads the same field locally, so dev environments and CI converge automatically.

## Implementation notes

- Pinned to `pnpm@10.33.2` (the exact version the workspace was bootstrapped with). Future bumps go through a dedicated `chore(deps): bump pnpm to X.Y.Z` PR that updates this field — keeps CI and local dev in lockstep.
- `corepack` will pick up this declaration on the next `corepack enable` or pnpm invocation. Devs already on 10.33.2 see no change; devs on a different version are nudged onto the canonical one.
- Workflow YAMLs (`.gitea/workflows/ci.yml`, `security-scheduled.yml`) untouched — `pnpm/action-setup@v3` reads `packageManager` directly.

## Verification

- [ ] Next CI run succeeds at `pnpm/action-setup@v3` (= the step that fails on smoke-test PR currently). Confirmed by re-pushing to the smoke-test branch (or any other PR) after this one merges.
- [x] `pnpm install` locally still works with the declaration (no change for someone already on 10.33.2).

## Related

- Follow-up to PR #4 (runner image fix). Together they unblock the CI gates.
- Smoke-test PR can be closed once a real PR (e.g. the upcoming "Local infra recipe") demonstrates green CI end to end.

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #6

package.json

@@ -2,6 +2,7 @@
   "name": "apf-portal",
   "version": "0.0.0",
   "license": "MIT",
+  "packageManager": "pnpm@10.33.2",
   "scripts": {
     "prepare": "husky",
     "ci:check": "pnpm exec nx affected -t format:check lint test build",