feat(infra): add local-dev Docker Compose stack (#57)

## Summary
Bring up Postgres + Redis + OTel Collector in one command so contributors can run the BFF end-to-end without manually wiring each service. Replaces the throwaway `docker run postgres:17-alpine` one-liner that was in `docs/development.md` §3.

### What lands
- **`infra/local/dev.compose.yml`** — three core services (`postgres:17.2-alpine`, `redis:7.4-alpine`, `otel/opentelemetry-collector-contrib:0.115.0`) plus two viewers gated behind Compose profiles:
  - `--profile dbtools` → `sosedoff/pgweb:0.16.2` (Postgres GUI on port 8081)
  - `--profile observability` → `jaegertracing/all-in-one:1.62` (Jaeger UI on 16686)
  - All ports overridable via `.env`. State in named volumes. Healthchecks on data services.
- **`infra/local/.env.example`** — credentials + ports template. `POSTGRES_PASSWORD` and `REDIS_PASSWORD` are mandatory (compose refuses to boot without them); other keys default sensibly.
- **`infra/local/init/postgres/01-init.sql`** — bootstrap SQL per **ADR-0013**: `audit_owner` / `audit_writer` / `audit_reader` / `audit_archiver` roles + `audit` schema. Default privileges encode the append-only contract (INSERT to writer, SELECT to reader, DELETE to archiver, no UPDATE/TRUNCATE to anyone). Applied on first Postgres boot only; documented re-run procedure.
- **`infra/local/otel-collector.yaml`** — pipeline: OTLP gRPC/HTTP → batch → debug exporter (always) + forward to `jaeger:4317`. When the observability profile is off, the Jaeger export logs warn-level retries but doesn't block the debug pipeline.

### Surrounding doc updates
- **`infra/README.md`** — new "Local-dev stack" section: service inventory, port table, first-time setup walkthrough, persistence/bootstrap-replay tips. The previous `local/` placeholder line is removed.
- **`docs/development.md`** §3 — rewritten to walk through the compose-based setup; cross-links to `infra/README.md` for the full reference. Roadmap entry for "Local infra recipe" removed from §8 (now implemented); "Observability dev-loop" line adjusted to point at the new Jaeger profile.

### Out of scope
- **Production parity** — HA Postgres, Redis Sentinel, real OTel backend (Tempo / Loki / etc.) — defer to the on-prem infrastructure ADR (phase 3b). The dev-only nature of this stack is called out explicitly in `infra/README.md`.
- **Wiring the BFF** to actually use these endpoints (NestJS config, Prisma datasource URL, OTel SDK init) — that's the **B — Observability foundations** chantier, next up.

## Test plan
- [ ] `cd infra/local && cp .env.example .env && docker compose -f dev.compose.yml up -d` → all three core services come up healthy; verify with `docker compose ps`.
- [ ] `psql postgres://portal:<pwd>@localhost:5432/portal_dev -c "\dn"` shows the `audit` schema; `\dg` shows the four audit roles.
- [ ] `redis-cli -a <pwd> PING` → `PONG`.
- [ ] Send a fake OTLP trace via grpcurl → see it printed by `docker compose logs otel-collector`.
- [ ] `--profile dbtools up -d` → http://localhost:8081 shows pgweb UI, can navigate to the audit schema.
- [ ] `--profile observability up -d` → http://localhost:16686 shows Jaeger UI; collector logs no longer report Jaeger export retries.
- [ ] `docker compose down -v` cleanly removes everything; next `up -d` re-runs the bootstrap SQL.

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #57

infra/local/.env.example

@@ -0,0 +1,28 @@
+# Local-dev secrets and ports for `infra/local/dev.compose.yml`.
+# Copy to `.env` (which is git-ignored) and adjust as needed.
+#
+#   cp .env.example .env
+#   $EDITOR .env
+
+# ---------------------------------------------------------------- Postgres
+# `POSTGRES_PASSWORD` is mandatory — the compose refuses to boot without it.
+POSTGRES_USER=portal
+POSTGRES_PASSWORD=portal_dev_change_me
+POSTGRES_DB=portal_dev
+POSTGRES_PORT=5432
+
+# ---------------------------------------------------------------- Redis
+# Same — mandatory.
+REDIS_PASSWORD=redis_dev_change_me
+REDIS_PORT=6379
+
+# ---------------------------------------------------------------- OTel
+OTEL_GRPC_PORT=4317
+OTEL_HTTP_PORT=4318
+
+# ---------------------------------------------------------------- Optional viewers
+# Only consumed when the matching Compose profile is activated:
+#   --profile dbtools       → pgweb
+#   --profile observability → Jaeger UI
+PGWEB_PORT=8081
+JAEGER_UI_PORT=16686