fix(infra): rename pgweb DATABASE_URL to PGWEB_DATABASE_URL (#62)

## Summary

pgweb 0.16 deprecated `DATABASE_URL` in favour of `PGWEB_DATABASE_URL`. With the old name, the container starts up, emits a `[DEPRECATION]` warning, then crashes:

```
[DEPRECATION] Usage of DATABASE_URL env var is deprecated, please use PGWEB_DATABASE_URL variable instead
Pgweb v0.16.2 ...
Error: Invalid URL. Valid format: postgres://user:password@host:port/db?sslmode=mode
```

— because the new code path reads `PGWEB_DATABASE_URL` (empty) and the URL parser rejects an empty string.

Rename the env key in the compose file. Same value, just the new name.

## Test plan

- [ ] After merge: `docker compose -f infra/local/dev.compose.yml --profile dbtools up -d` → pgweb stays running (not in `Restarting` loop).
- [ ] http://localhost:8081 loads pgweb's UI; click through to the `audit` schema and the four `audit_*` roles to confirm DB connection.

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #62

infra/local/dev.compose.yml

@@ -103,7 +103,10 @@ services:
     restart: unless-stopped
     profiles: [dbtools]
     environment:
-      DATABASE_URL: postgres://${POSTGRES_USER:-portal}:${POSTGRES_PASSWORD}@postgres:5432/${POSTGRES_DB:-portal_dev}?sslmode=disable
+      # `PGWEB_DATABASE_URL` (formerly `DATABASE_URL`) — pgweb 0.16
+      # deprecated the old name, ignores it, and starts up empty,
+      # crashing with "Invalid URL".
+      PGWEB_DATABASE_URL: postgres://${POSTGRES_USER:-portal}:${POSTGRES_PASSWORD}@postgres:5432/${POSTGRES_DB:-portal_dev}?sslmode=disable
     ports:
       - '${PGWEB_PORT:-8081}:8081'
     depends_on: