fix(gitignore): ignore infra/*-tenant.personas.json (ADR-0026) (#268)

## Summary

Add `infra/*-tenant.personas.json` to `.gitignore` mirroring the existing `*-tenant.entra.json` pattern, so the per-persona Entra `oid` map consumed by `apps/portal-bff/prisma/seed.ts` (ADR-0026) cannot accidentally be committed. The schema template `infra/test-tenant.personas.example.json` was already in place; the matching ignore was missed when the personas file was introduced.

## Background

ADR-0026 §"Seed personas" introduced two parallel tenant-private files:

- **`*-tenant.entra.json`** — Entra security-group GUIDs → role-slug map (24 entries). Has been correctly ignored since shipped (`.gitignore` lines 34-36).
- **`*-tenant.personas.json`** — Per-persona Entra `oid` map (19 entries). The example template was committed correctly but the matching ignore pattern was never added.

Practical consequence: `infra/test-tenant.personas.json` has been showing up as untracked (`??`) in `git status` on the R&D Lead's machine since the seed personas work landed in late May, surviving multiple sessions and PR opens — and could have been accidentally `git add .`-ed at any point. Confirmed via `git log --all -- infra/test-tenant.personas.json` (empty) that no commit has touched it yet, so no history rewrite needed — pure forward-only fix.

## What lands

| File | Change |
| --- | --- |
| `.gitignore` | Three new lines mirroring the entra pattern: a comment, `infra/*-tenant.personas.json` (ignore), `!infra/*-tenant.personas.example.json` (keep the template tracked). |
| `infra/README.md` | New row in the top-level table for the per-persona oid map, pointing at the `.example.json` template and ADR-0026, right under the existing entra row. |

## Verification

- [x] `git check-ignore -v infra/test-tenant.personas.json` → matched by `.gitignore:40:infra/*-tenant.personas.json`.
- [x] `git check-ignore -v infra/test-tenant.personas.example.json` → not ignored (the `!` negation correctly preserves the example template as a tracked file).
- [x] `git status --short` no longer surfaces the `??` for the personas file.
- [x] `git log --all -- infra/test-tenant.personas.json` confirms zero commits ever referenced this path, so no `git rm --cached` or history rewrite is required.

## Related

- [ADR-0025](docs/decisions/0025-authorization-model-privileges-roles-scopes.md) — entra group map, the pattern this PR copies.
- [ADR-0026](docs/decisions/0026-person-user-portal-data-model.md) — Person/User/UserScope seed which consumes the personas map.

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #268

.gitignore

@@ -35,6 +35,11 @@ pnpm-debug.log*
 infra/*-tenant.entra.json
 !infra/*-tenant.entra.example.json
 
+# Tenant-private Entra per-persona oids consumed by prisma/seed.ts
+# (ADR-0026 §"Seed personas"). Same pattern — commit only the example.
+infra/*-tenant.personas.json
+!infra/*-tenant.personas.example.json
+
 # OS / editor scrap
 .DS_Store
 Thumbs.db