docs: archive the finished backlogs (RD-30)

Two backlog trees are complete: `docs/project/backlog/` (75 files, every
WP done) and `docs/project/refactor-backlog-setup/` (the arc before it).
Move both under `docs/project/archive/` with `git mv`, so history stays
intact through `git log --follow`. `SHOWCASE-ROADMAP.md` moves with them,
because it points at the now-archived backlog README.

Add `docs/project/archive/README.md`. It states that these trees are
historical and names the two directories that are still live.

Repoint every inbound reference named in RD-30's Files table: CLAUDE.md,
the root README, both backend READMEs, `LetterHtml.cs`, `a11y.mdx`, the
`document-feature` and `new-ssp` skills, and the readable-codebase PLAN,
README, and RD-19 ticket. Fix two upward-relative links inside the moved
WP files (WP-68, WP-69) that gained a directory level and would otherwise
break. Repoint `.prettierignore`'s two agent-prompt exclusions to their
new path, so prettier keeps leaving those files' exact wording alone.

Mark RD-30 done and check off its acceptance criteria; flip its README
row to done.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/project/archive/backlog/WP-38-dependency-graph-boundaries.md

@@ -0,0 +1,49 @@
+# WP-38 — Dependency graph + declarative boundaries
+
+Status: done
+Phase: 8 — platform/DX/showcase
+Priority: P1
+
+## Outcome
+
+Adopted **dependency-cruiser**. `.dependency-cruiser.js` is the single declarative source for
+context + layer boundaries (incl. the previously-missing `herregistratie` scope + no-circular);
+`npm run dep:check` enforces (wired into `ci-local.sh` + the `frontend` CI job), `npm run dep:graph`
+emits a mermaid context×layer graph to `docs/reference/architecture/dependency-graph.md`. The
+per-context `no-restricted-imports` blocks were **removed** from `eslint.config.mjs` (now only
+`no-explicit-any` + template a11y remain); parity verified by planting violations (domain→Angular,
+beheer→registratie incl. type-only) and confirming `dep:check` flags them. Doc:
+`docs/reference/architecture/dependencies.md`; `new-context` skill updated to the single source.
+
+## Why
+
+Bounded-context + atomic-layer boundaries are enforced only by hand-duplicated
+`no-restricted-imports` blocks in `eslint.config.mjs` — pass/fail, no graph, and brittle: the
+`new-context` skill literally says "grep the config and copy a block", and `herregistratie` is
+missing its explicit ban block (asymmetry). We want to **see** the dependencies AND **enforce**
+them from one declarative source.
+
+## Decisions
+
+- **Step 1 — tool fork:** dependency-cruiser (recommended: graph + CI rules on plain Angular) vs
+  Sheriff (tag-based, DDD/atomic-native, weaker graph). Decide before building.
+- Encode context + layer rules once (contexts `shared/auth/registratie/herregistratie/brief/beheer/
+showcase`; layers `domain/application/infrastructure/contracts/ui`); **fix the herregistratie gap**.
+- Keep ESLint for the intra-file rules it does better (`domain↛@angular`, ApiClient value-import
+  confinement, `no-explicit-any`); migrate only the cross-module _direction_ rules to the new tool.
+- Emit a graph the showcase/teaching can reuse (feeds WP-39).
+
+## Files
+
+- New: `.dependency-cruiser.js` (or `sheriff.config.ts`); `npm run graph` + validate script.
+- `scripts/ci-local.sh` + `.github/workflows/ci.yml` — add `depcruise --validate` (non-optional).
+- `eslint.config.mjs` — remove the migrated direction rules (keep the rest).
+- New doc `docs/reference/architecture/dependencies.md`; embed the graph in a Foundations page.
+- `.claude/skills/new-context/SKILL.md` — point at the single declarative source.
+
+## Acceptance criteria
+
+- [x] One declarative config expresses all allowed context/layer edges; herregistratie included.
+- [x] `npm run dep:graph` produces a committed mermaid architecture graph; `dep:check` runs in `npm run ci`.
+- [x] A deliberately-illegal import fails the validate step (proven, then reverted).
+- [x] No loss of enforcement vs the old ESLint blocks; `npm run ci` green.