feat(portal-bff): observability foundations (Pino + CLS + OTel) (#70)

## Summary

Implements ADR-0012 phase 1, BFF side. The SPA wiring is a separate phase-2 PR.

The BFF now emits structured JSON logs to stdout, tagged with `trace_id` / `span_id` from the active OTel context, and exports OTLP traces over HTTP/Protobuf to the Collector that already runs in the local-dev compose. Anything Nest, Express, HTTP-out, Prisma (Postgres) or `ioredis` does is auto-spanned. A `GET /api/health` liveness endpoint is added to round things out.

## What lands

**Runtime libs added** (production deps):

- `nestjs-pino`, `pino`, `pino-http` — structured logging
- `nestjs-cls` — request-scoped context
- `@opentelemetry/api` / `sdk-node` / `resources` / `semantic-conventions`
- `@opentelemetry/exporter-trace-otlp-proto` (HTTP/Protobuf, port 4318)
- `@opentelemetry/instrumentation-{http,express,nestjs-core,pg,ioredis,pino}` — curated, **no** `auto-instrumentations-node` mass-import (anti-bricolage)

Dev: `pino-pretty` (gated by `NODE_ENV`).

**Code:**

- `apps/portal-bff/src/observability/tracing.ts` — OTel `NodeSDK` bootstrap. Documents the load-order constraint inline (must be the very first import of `main.ts`). Pure side-effect module.
- `apps/portal-bff/src/observability/observability.module.ts` — composes `ClsModule` (UUID per request stored as `request_id`) and `LoggerModule` (`pino-pretty` in dev, raw JSON in prod, `LOG_LEVEL` env-driven, `/health` excluded from auto-logging, `X-Request-Id` honoured if inbound).
- `apps/portal-bff/src/health/{health.controller,health.module,health.controller.spec}.ts` — `GET /api/health` returning `{status, uptimeSeconds, service, version}`. Cheap liveness only — `/readiness` lands when dependencies have a readiness story.
- `apps/portal-bff/src/config/check-database-url.{ts,spec.ts}` — fail-fast validator called from `main.ts` before NestFactory boots. Catches the same family of bug that bit pgweb in #63: a literal special character in `POSTGRES_PASSWORD` that needs URL-encoding in `DATABASE_URL`. Prisma requires a URL string (no discrete-flag escape hatch), so early validation + a clear error message is the v1 mitigation. Six unit tests cover happy path, missing URL, wrong scheme, encoded special chars, literal `@` in password, malformed URL.

**Wiring:**

- `main.ts` imports `./observability/tracing` as line 1, then uses `app.get(Logger)` from `nestjs-pino` with `bufferLogs: true` so early-bootstrap lines are not lost.
- `app.module.ts` imports `ObservabilityModule` first, then `PrismaModule`, then `HealthModule`.
- `apps/portal-bff/.env.example` promotes `LOG_LEVEL`, `OTEL_SERVICE_NAME`, `OTEL_SERVICE_VERSION`, `OTEL_EXPORTER_OTLP_ENDPOINT`, `OTEL_EXPORTER_OTLP_PROTOCOL`, `OTEL_TRACES_SAMPLER` from the "future" comment to active settings — defaults target the local-dev Collector.
- Both `apps/portal-bff/.env.example` and `infra/local/.env.example` now spell out the URL-encoding constraint on `POSTGRES_PASSWORD` with the char-by-char encoding table (`@` → `%40`, etc.).

**ADR-0012 §Confirmation** rewritten to distinguish what landed in this PR from what is wired as the corresponding feature ADRs ship (CLS keys for `session_id` / `user_id_hash` / `audience`, `LOG_USER_ID_SALT` enforcement, redact list, custom spans, SPA-side SDK, full integration tests, prod Collector config).

## Trace ↔ log correlation

Automatic via `@opentelemetry/instrumentation-pino` — every Pino record gets `trace_id` and `span_id` injected from the active OTel context. No CLS gymnastics needed for that concern.

## Verification

```bash
pnpm exec nx run-many -t lint test build       # 8 projects green
pnpm audit --audit-level=moderate              # 0 vulnerabilities
./infra/local/dev.sh up observability          # start Collector + Jaeger
cp apps/portal-bff/.env.example apps/portal-bff/.env
pnpm nx serve portal-bff
curl http://localhost:3000/api/health
# → {"status":"ok","uptimeSeconds":N,"service":"portal-bff","version":"dev"}
```

Then hit `GET http://localhost:3000/api` once or twice and open http://localhost:16686 — the corresponding spans appear in Jaeger, and Pino logs on stdout carry the matching `trace_id`.

## Test plan

- [ ] `nx run-many -t lint test build` green on this PR's CI run.
- [ ] `pnpm audit` clean.
- [ ] BFF boots, `/api/health` returns the expected JSON.
- [ ] Pino logs in dev are colourised one-liners; in prod they would be raw JSON (toggled by `NODE_ENV=production`).
- [ ] With the local-dev stack's `--profile observability` active, traces are visible in Jaeger UI.
- [ ] Each Pino log line for a request carries the same `trace_id` as the trace span in Jaeger.

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #70

apps/portal-bff/.env.example

@@ -4,7 +4,35 @@
 
 # Postgres connection (per ADR-0006)
 # Local dev default: dockerised Postgres on port 5432, schema 'public'.
-DATABASE_URL="postgresql://portal:portal@localhost:5432/portal_dev?schema=public"
+# Username / password / db must match infra/local/.env (POSTGRES_USER /
+# POSTGRES_PASSWORD / POSTGRES_DB) — those are the source of truth,
+# this is the BFF view of the same connection.
+#
+# IMPORTANT — URL encoding. The password is part of the URL userinfo
+# segment, so any of these characters must be URL-encoded:
+#     @ → %40    # → %23    : → %3A    / → %2F    ? → %3F
+#     % → %25    & → %26    = → %3D    + → %2B    ; → %3B
+# i.e. if your POSTGRES_PASSWORD is "p@ss#1", DATABASE_URL must read
+# "postgresql://portal:p%40ss%231@localhost:5432/portal_dev?schema=public"
+# The BFF aborts at boot with a clear error if it detects an unencoded
+# special character (see apps/portal-bff/src/config/check-database-url.ts).
+DATABASE_URL="postgresql://portal:portal_dev_change_me@localhost:5432/portal_dev?schema=public"
+
+# Observability (per ADR-0012)
+# All OTEL_* keys are honoured by the OpenTelemetry SDK directly — see
+# apps/portal-bff/src/observability/tracing.ts for the bootstrap.
+# Pino log level: 'info' in prod, 'debug' in dev (default if unset).
+LOG_LEVEL=debug
+OTEL_SERVICE_NAME=portal-bff
+OTEL_SERVICE_VERSION=dev
+# Default endpoint targets the Collector provisioned in
+# infra/local/dev.compose.yml. The /v1/traces suffix is required by
+# the HTTP/Protobuf transport.
+OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318/v1/traces
+OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf
+# v1 samples 100 % at the app; tail sampling is delegated to the
+# Collector (per ADR-0012). Override only for spike investigations.
+OTEL_TRACES_SAMPLER=always_on
 
 # Future env vars introduced by upcoming phases / ADRs:
 #
@@ -28,15 +56,9 @@ DATABASE_URL="postgresql://portal:portal@localhost:5432/portal_dev?schema=public
 # MFA (ADR-0011):
 #   MFA_FRESHNESS_SECONDS           (default 600)
 #
-# Observability (ADR-0012):
-#   LOG_LEVEL                       ('info' in prod, 'debug' in dev)
-#   LOG_USER_ID_SALT                (per-environment salt)
-#   OTEL_SERVICE_NAME               ('portal-bff')
-#   OTEL_SERVICE_VERSION
-#   OTEL_RESOURCE_ATTRIBUTES
-#   OTEL_EXPORTER_OTLP_ENDPOINT
-#   OTEL_EXPORTER_OTLP_PROTOCOL     ('http/protobuf')
-#   OTEL_TRACES_SAMPLER             ('always_on' in v1)
+# Observability — additional keys to be wired as features land:
+#   LOG_USER_ID_SALT                (per-environment salt for hashing user_id
+#                                    in CLS context — needed once auth lands)
 #
 # Audit trail (ADR-0013):
 #   AUDIT_DATABASE_URL              (separate creds, role 'audit_writer')