docs(decisions): add ADR-0030 dockerised full-stack dev mode (proposed) (#256)

## Summary

Propose **ADR-0030 — Dockerised full-stack dev mode**: an `apps` Compose profile that runs the three Nx apps (`portal-bff`, `portal-shell`, `portal-admin`) from a shared `Dockerfile.dev`, so a developer can `docker compose up` the whole stack with **no native Node/pnpm** on the host.

`proposed` status — this PR is the **decision record only**. The `Dockerfile.dev` + the `apps` profile + the BFF entrypoint land in a follow-up PR once the ADR is accepted.

## Why

Two frictions motivate it:
1. Infra is already in Docker (`infra/local/dev.compose.yml`), but the Nx apps run natively — every dev pays the nvm/corepack/pnpm setup cost. The recent fresh-VM `.zshrc` nvm gap is a concrete example of that path breaking.
2. A developer asked to run all servers with a single `docker compose up`, no toolchain, no IDE attach.

## Decision (chosen option)

An **`apps` Compose profile** backed by **one shared `Dockerfile.dev`** (node:24 + pinned pnpm), because it is purely additive:
- `./infra/local/dev.sh up` stays infra-only (native + devcontainer flows unchanged).
- `./infra/local/dev.sh up apps` brings up infra + the three dev servers with hot reload.

Key design points captured in the ADR (built in the follow-up): one image / one install for the monorepo; repo bind-mounted but `node_modules` + Nx cache in **named volumes** (native-module arch correctness); `depends_on … service_healthy`; BFF entrypoint does `prisma generate` + `migrate deploy`; services point at the existing `apf-portal-dev` Compose network.

The ADR documents a "which mode when" table so the **three** dev modes (native / devcontainer / compose-`apps`) coexist without confusion.

## Scope guardrails

- **Dev-only.** No production images here — those are tracked against the ADR-0028 Container Registry follow-up (post-cutover). The ADR is explicit that it produces no deployment artefact.
- Complements ADR-0020's devcontainer (interactive/IDE) with a non-interactive services sibling; does not replace it.

## Numbering

Takes **0030**, not 0029. `0029` is reserved for the cascade/Pléiades/Acteurs+ syncs ADR (referenced by ADR-0026/0027/0028); numbers are never reused, so the dev-mode ADR takes the next free slot. The index gap at 0029 is intentional until that ADR is written.

## What lands

| File | Change |
| --- | --- |
| `docs/decisions/0030-dockerised-dev-mode.md` | New ADR, `proposed`. |
| `docs/decisions/README.md` | Index row for 0030. |

## Test plan

- [x] MADR 4.0.0 frontmatter; tags drawn from the README vocabulary (`infrastructure`, `process`).
- [x] Index updated in the same commit (per the repo's index-maintenance rule).
- [ ] R&D Lead review → accept / revise. On acceptance: update the CLAUDE.md architecture roll-up + add the "which mode when" guidance to `docs/setup/`, then open the implementation PR.

## Related

- [ADR-0020](docs/decisions/0020-portal-admin-app.md) — VSCode devcontainer (the interactive no-toolchain path this complements).
- [ADR-0028](docs/decisions/0028-migrate-cicd-and-git-hosting-to-gitlab.md) — Container Registry / production images (the deferred prod-image work).
- [ADR-0006](docs/decisions/0006-persistence-postgresql-prisma.md) — Prisma; the entrypoint applies (never authors) migrations.

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #256

docs/decisions/README.md

@@ -72,3 +72,4 @@ ADRs are listed in numerical order. To slice by topic, filter on the `Tags` colu
 | [0026](0026-person-user-portal-data-model.md)                | `Person` golden record + `User` portal-account — portal-side identity model                                      | accepted | `data`, `backend`, `security`                                  | 2026-05-24 |
 | [0027](0027-portal-side-organisational-hierarchy.md)         | Portal-side organisational hierarchy — `Structure` with kind discriminator and nullable FINESS / SIRET           | accepted | `data`, `backend`                                              | 2026-05-24 |
 | [0028](0028-migrate-cicd-and-git-hosting-to-gitlab.md)       | Migrate CI/CD + git hosting from Gitea to GitLab self-hosted                                                     | accepted | `infrastructure`, `process`                                    | 2026-05-26 |
+| [0030](0030-dockerised-dev-mode.md)                          | Dockerised full-stack dev mode — `compose up` runs the Nx apps alongside infra                                   | proposed | `infrastructure`, `process`                                    | 2026-05-28 |