docs(backlog): split S-00 into S-00-a..e (refs #1)

Mirror the S-00 split into the backlog: replace the single S-00 slice
with sub-slices S-00-a (BFF + health), S-00-b (Docker + compose + smoke),
S-00-c (Gitea Actions CI), S-00-d (contributor workflow), and S-00-e
(docs scaffold). Source of truth remains Gitea; #1 is closed by
tools/split-s00.sh with a comment pointing at the replacements.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

BACKLOG.md

@@ -12,22 +12,41 @@ Each slice is **independently demoable** and meets the Definition of Done in `CL
 
 ## Iteration 0 — Foundations *(milestone: `Iteration 0 — Foundations`)*
 
-### S-00 · Repository skeleton, Gitea Actions CI, contributor workflow
+> **S-00 was split** (CLAUDE.md §13) into the sub-slices below. The original
+> outcome — a fresh clone + `docker compose up` reaching a green BFF health
+> endpoint, with CI green and the contributor scaffolding in place — is the sum
+> of S-00-a…e. Milestones, labels, and the Iteration 1 population are already
+> done (see `tools/seed-gitea.sh`).
 
-**Outcome:** A fresh `git clone` from the Respellion Gitea remote, followed by `docker compose up`, produces a green "hello world" health endpoint from a placeholder BFF. Gitea Actions runs lint, build, unit tests, and the compose-up smoke test, all green. Issue templates, PR template, milestones, labels, and the first project board exist in Gitea.
+### S-00-a · Placeholder BFF + health endpoint
 
-**Acceptance:**
+**Outcome:** A minimal .NET BFF exposing `GET /health` returning green; runnable with `dotnet run`. TDD anchor for the slice.
 
-- New developer follows `README.md` and reaches a green local environment in under 10 minutes.
+**Touches:** `services/bff/`, tests. **Out of scope:** Docker, CI, OIDC.
-- Gitea Actions pipeline green on `main`.
-- `git-cliff` produces an empty `CHANGELOG.md`.
-- `docs/PRD.md`, `CLAUDE.md`, `BACKLOG.md`, `docs/architecture/adr-0001-loose-coupling.md`, `docs/gitea-workflow.md` all in repo.
-- `.gitea/workflows/ci.yaml`, `.gitea/ISSUE_TEMPLATE/{slice,bug,adr-proposal}.md`, `.gitea/PULL_REQUEST_TEMPLATE.md` all in repo.
-- Gitea milestone `Iteration 1 — Walking Skeleton` exists, populated with issues S-01 through S-09.
 
-**Touches:** repo layout, Gitea Actions workflows, Dockerfile for placeholder BFF, `docker-compose.yml` skeleton, MkDocs scaffold, Gitea issue/PR templates.
+### S-00-b · Dockerfile + compose skeleton + compose-up smoke
 
-**Out of scope:** any business logic, frontend, OpenZaak.
+**Outcome:** BFF containerized; `infra/docker-compose.yml` brings it up; health green within 3 minutes from a fresh clone.
+
+**Touches:** `services/bff/Dockerfile`, `infra/docker-compose.yml`, smoke script. **Out of scope:** other services, CI.
+
+### S-00-c · Gitea Actions CI (lint, build, unit, compose-up smoke)
+
+**Outcome:** `.gitea/workflows/ci.yaml` green on PRs and `main`: lint, build, unit, compose-up smoke. Actions pinned by absolute URL (§8.7/§15).
+
+**Touches:** `.gitea/workflows/ci.yaml`, `docs/runbooks/ci.md`. **Out of scope:** mutation, e2e, container push.
+
+### S-00-d · Contributor workflow: issue/PR templates, git-cliff, CHANGELOG
+
+**Outcome:** Issue templates (`slice`/`bug`/`adr-proposal`), PR template, `git-cliff` → empty `CHANGELOG.md`, `docs/gitea-workflow.md`.
+
+**Touches:** `.gitea/ISSUE_TEMPLATE/`, `.gitea/PULL_REQUEST_TEMPLATE.md`, `cliff.toml`, `CHANGELOG.md`, `docs/gitea-workflow.md`. **Out of scope:** app code.
+
+### S-00-e · Docs scaffold: MkDocs + ADR-0001 + README quickstart
+
+**Outcome:** MkDocs builds the `docs/` site; `docs/architecture/adr-0001-loose-coupling.md` exists; README has a sub-10-minute quickstart.
+
+**Touches:** `mkdocs.yml`, `docs/` nav, `docs/architecture/adr-0001-loose-coupling.md`, `README.md`. **Out of scope:** Gitea Pages publish.
 
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