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-15-missing-stories.md

@@ -0,0 +1,64 @@
+# WP-15 — Missing stories: shell + brief components
+
+Status: todo
+Phase: 3 — Storybook as curriculum
+Depends on: WP-14 (titles), WP-01 (axe gate covers the new stories automatically)
+
+## Why
+
+"UI is exercised via Storybook stories" (CLAUDE.md §5) — but 7 components have none:
+`shared/layout/shell` and six of seven brief components. Unstoried components are also
+invisible to the axe gate.
+
+## Read first
+
+- `src/app/brief/ui/letter-composer/letter-composer.stories.ts` (the one brief story —
+  fixture + decorator pattern to reuse)
+- The seven components below
+
+## Decisions (pre-made, don't relitigate)
+
+- Titles per WP-14 scheme: `Design System/Templates/Shell`, `Domein/Brief/<Name>`.
+- If fixture duplication across brief stories bites, extract a shared
+  `src/app/brief/ui/brief.fixtures.ts` — otherwise keep fixtures co-located.
+
+## Files (new)
+
+- `src/app/shared/layout/shell/shell.stories.ts`
+- `src/app/brief/ui/rejection-comments/rejection-comments.stories.ts`
+- `src/app/brief/ui/diagnostics-panel/diagnostics-panel.stories.ts`
+- `src/app/brief/ui/letter-block/letter-block.stories.ts`
+- `src/app/brief/ui/letter-preview/letter-preview.stories.ts`
+- `src/app/brief/ui/letter-section/letter-section.stories.ts`
+- `src/app/brief/ui/passage-picker/passage-picker.stories.ts`
+
+## Steps
+
+1. One story file per component: default state + at least one meaningful variant
+   (e.g. letter-block locked/editable, diagnostics with findings/empty, rejection-comments
+   filled, preview with sample data toggle).
+2. Provide router/HTTP/store context via `applicationConfig`/`moduleMetadata` decorators
+   like the wizard stories do.
+3. Run the axe gate; fix trivial violations in the components (label/role level); anything
+   structural → escape hatch + cross-ref WP-16.
+
+## Acceptance criteria
+
+- [ ] Every component in `src/app` has ≥1 story (verify: list components without a
+      co-located `*.stories.ts`; expect zero, pages excepted if that's the existing
+      norm — note the norm in this file when checked).
+- [ ] All new stories pass the axe gate (or carry a justified skip).
+- [ ] Titles follow WP-14.
+
+## Verification
+
+GREEN + `npm run test-storybook:ci`.
+
+## Out of scope
+
+Play-test assertions (WP-16 adds those where they enforce a contract).
+
+## Risks
+
+Brief components may lean on `BriefStore` state — stub via the store's public API in a
+decorator rather than reaching into internals.