docs: replace SHOWCASE-ROADMAP.md with docs/backlog/ (17 WPs)

Turns the prior roadmap sketch into ordered, gated work packages (enforcement
gates, FP/DDD consistency, CIBG fidelity, Storybook curriculum, a11y) from the
2026-07-02 showcase-hardening audit.

docs/backlog/WP-07-brief-idioms.md

@@ -0,0 +1,70 @@
+# WP-07 — Brief on the shared idioms + RemoteData MDX
+
+Status: todo
+Phase: 1 — FP/DDD core
+Depends on: WP-06 (typed `<app-async>`)
+
+## Why
+
+The brief context drifted from the repo's own reflexes: `brief.store.ts` (~lines 22-25)
+holds `busy: signal<boolean>` + `lastError: signal<string|null>` + a separate `saveState`
+union side by side — representable illegal combos, the exact "second boolean" smell
+CLAUDE.md §3 bans. And `brief.page.ts` hand-renders its load lifecycle with `@switch` +
+spinner/alert instead of `RemoteData` + `<app-async>` — the only async flow in the app
+bypassing the shared molecule.
+
+## Read first
+
+- `CLAUDE.md` §3; `src/app/shared/application/remote-data.ts`
+- `src/app/brief/application/brief.store.ts`, `src/app/brief/ui/brief.page.ts`,
+  `src/app/brief/domain/brief.machine.ts` (+ spec)
+- `src/app/registratie/application/applications.store.ts` (a store doing it right)
+
+## Decisions (pre-made, don't relitigate)
+
+- Transient submit/save state becomes **one** tagged union
+  (`Idle | Busy | Failed{error}`), replacing `busy`+`lastError`. `saveState` keeps its
+  union shape (align tag style).
+- Load lifecycle → `RemoteData` + `<app-async>`; the machine keeps owning the letter's
+  *domain* lifecycle (loading tags move out of the machine only if they purely mirror
+  the fetch — keep the seam: RemoteData = fetch, machine = letter).
+- Keep the debounced-save sequencing identical; only re-type the state.
+
+## Files
+
+- `src/app/brief/application/brief.store.ts`
+- `src/app/brief/ui/brief.page.ts`
+- `src/app/brief/domain/brief.machine.ts` + `brief.machine.spec.ts`
+- New `src/docs/remote-data.mdx` — title `Foundations/RemoteData & Async`
+
+## Steps
+
+1. Replace the signal trio with one union signal; update consumers (letter-composer bar,
+   autosave status line).
+2. Route the page's load through `RemoteData` + `<app-async>` (typed via WP-06); wire the
+   existing loading/empty/failure templates.
+3. Update machine/store specs for the union transitions.
+4. MDX page: the four states, `map2`/`andThen`, the delay-gated spinner, and the
+   `?scenario=` dev toggle — linking `brief.page.ts` and `dashboard.page.ts` as live
+   examples.
+
+## Acceptance criteria
+
+- [ ] No boolean-plus-error signal pairs in `brief/`.
+- [ ] `/brief` renders all four async states (check with `?scenario=slow|empty|error`).
+- [ ] Specs cover the transition union (Busy→Failed, Busy→Idle).
+- [ ] MDX renders under Foundations.
+
+## Verification
+
+GREEN + `npm run test-storybook:ci`. Manual: `npm start` → `/brief` with
+`?scenario=slow`, `?scenario=error`; exercise autosave + submit + rejection flow.
+
+## Out of scope
+
+Brief component stories (WP-15); machine renaming conventions (WP-08).
+
+## Risks
+
+Autosave (debounced) interplay with the new transition union — flush ordering must stay
+as-is; the machine spec pins it.