docs: reorganize into project/ + reference/, expand Storybook Foundations

Move working docs (backlog, prd, roadmap) under docs/project/ and durable
docs (architecture ADRs, guides, audits) under docs/reference/; add a
docs/README.md index. Update every path reference in code comments, CLAUDE.md,
READMEs, and the new-ssp skill. Expand the Storybook Foundations curriculum
(Overview, BDD, i18n; rename Layers→Domain-Driven Design) and reorder the sidebar.

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

docs/reference/architecture/ARCHITECTURE.md

@@ -10,7 +10,7 @@ professional logs in, sees their registration, and can apply for
 re-registration — "herregistratie").
 
 > New to functional programming or The Elm Architecture? Start with the progressive
-> learning guide [`fp-tea-atomic-design.md`](./fp-tea-atomic-design.md), which teaches
+> learning guide [`fp-tea-atomic-design.md`](../fp-tea-atomic-design.md), which teaches
 > the concepts (with Elm ↔ this-app examples) and the recipes; this document is the
 > reference deep-dive it points back to.
 

docs/reference/fp-tea-atomic-design.md

@@ -17,7 +17,7 @@ feature." A senior can skim Parts 1–4 and jump to **Part 5** (FP × atomic des
 defined in plain words on first use and again in the **glossary** (Part 8).
 
 This guide is the _teaching_ layer. For the reference deep-dives it points to
-[`ARCHITECTURE.md`](./ARCHITECTURE.md) and
+[`ARCHITECTURE.md`](./architecture/ARCHITECTURE.md) and
 [ADR-0001](./architecture/0001-bff-lite-decision-dtos.md) rather than repeating them.
 Every code snippet below is real code from this repo, with its file path.
 
@@ -127,7 +127,7 @@ Two kinds of type do most of the work:
 
 The decisive move is choosing types so that **illegal states can't be written down**.
 Compare three booleans (2³ = 8 combinations, most nonsense) with one union of the 4 real
-states — see [`ARCHITECTURE.md` §2a](./ARCHITECTURE.md#2a-remotedata--one-value-instead-of-three-booleans)
+states — see [`ARCHITECTURE.md` §2a](./architecture/ARCHITECTURE.md#2a-remotedata--one-value-instead-of-three-booleans)
 for the full `RemoteData` treatment and diagram. The wizard's own Model is the same
 idea (`herregistratie.machine.ts`):
 
@@ -216,7 +216,7 @@ This app implements TEA with Angular **signals**. There is no extra state librar
 important shape difference from textbook Elm: **state is per-wizard, not one global
 Model** — each flow (`herregistratie`, `intake`, `registratie`) has its own little
 store. Cross-page state that _must_ be shared lives in one root singleton
-(`BigProfileStore`, see [`ARCHITECTURE.md` §2e](./ARCHITECTURE.md#2e-optimistic-update--rollback-and-shared-state-across-pages)).
+(`BigProfileStore`, see [`ARCHITECTURE.md` §2e](./architecture/ARCHITECTURE.md#2e-optimistic-update--rollback-and-shared-state-across-pages)).
 
 ### 4a. The store — TEA's runtime in ~10 lines
 
@@ -424,7 +424,7 @@ Molecules compose atoms; organisms compose molecules — exactly like composing
 functions, where the composite is still pure. `address-fields` is pure because the
 `form-field` and `text-input` it's built from are pure. Each atomic level only uses the
 level(s) below it (see the hierarchy diagram in
-[`ARCHITECTURE.md` §1](./ARCHITECTURE.md#1-the-big-picture-three-contexts-four-layers)).
+[`ARCHITECTURE.md` §1](./architecture/ARCHITECTURE.md#1-the-big-picture-three-contexts-four-layers)).
 
 ### 5c. Pages / containers are the TEA runtime (the shell)
 
@@ -474,7 +474,7 @@ Each property maps to a tangible benefit you can point at in this repo:
 - **Illegal states won't compile.** `Submitting` carries `Valid` data and has no `errors`
   field, so "submit with errors showing" is unwritable. A whole bug class disappears
   before runtime — contrast the 8-state boolean soup in
-  [`ARCHITECTURE.md` §2a](./ARCHITECTURE.md#2a-remotedata--one-value-instead-of-three-booleans).
+  [`ARCHITECTURE.md` §2a](./architecture/ARCHITECTURE.md#2a-remotedata--one-value-instead-of-three-booleans).
 
 - **Pure presentational components.** `address-fields` is tested by inputs → DOM and
   reused in two call-sites (the registratie wizard and the change-request form) with no
@@ -500,7 +500,7 @@ Each recipe follows the existing pattern and naming, and ends with the same remi
 ### Recipe A — Add an atomic component (atom / molecule / organism)
 
 **When:** you genuinely need a new building block (not a one-off; reuse must earn it —
-see [CLAUDE.md §2](../CLAUDE.md)).
+see [CLAUDE.md §2](../../CLAUDE.md)).
 
 **Where:** `shared/ui/` if generic; a context's `ui/` if domain-specific. Pick the level
 by composition: composes nothing → **atom**; composes atoms → **molecule**; composes
@@ -634,7 +634,7 @@ _This is the same loop, again — now nested inside the wizard._
 
 ---
 
-_See also:_ [`ARCHITECTURE.md`](./ARCHITECTURE.md) (reference deep-dive on RemoteData,
+_See also:_ [`ARCHITECTURE.md`](./architecture/ARCHITECTURE.md) (reference deep-dive on RemoteData,
 the store, parse-don't-validate, and the .NET backend seam) and
 [ADR-0001](./architecture/0001-bff-lite-decision-dtos.md) (the BFF-lite + decision-DTO
 decision). Live demo: `/concepts` in the running app.