docs(skills): extract house recipes as Claude Code skills for SSP templating

8 template-generic skills in .claude/skills/ (new-feature, new-context,
value-object, form-machine, bff-endpoint, mutation-command, ui-component,
new-ssp), condensed from CLAUDE.md/ARCHITECTURE/fp-tea/ADRs and pointing at
this repo's worked examples. CLAUDE.md gains a pointer.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude/skills/mutation-command/SKILL.md

@@ -0,0 +1,58 @@
+---
+name: mutation-command
+description: Add a write/submit operation — infrastructure adapter method plus an application command factory returning Result, keeping the reducer pure. Use for any POST/PUT/DELETE a form or action triggers.
+---
+
+# Mutation command
+
+Reducer = "what the new state is"; command = "go do it, then say what happened".
+The UI holds an application command, never the network client (lint-enforced).
+
+## Skeleton
+
+**Adapter method** (`<context>/infrastructure/<name>.adapter.ts`) — takes the
+machine's `Valid` type, returns the server's answer, no parse (server is authority):
+
+```ts
+@Injectable({ providedIn: 'root' })
+export class ChangeRequestAdapter {
+  private client = inject(ApiClient);
+  async changeRequest(data: Valid): Promise<string> { /* → server reference */ }
+}
+```
+
+**Command factory** (`<context>/application/submit-<name>.ts`) — binds the adapter in
+an injection context; `runSubmit` is the one try/catch + ProblemDetails mapping:
+
+```ts
+export function createSubmitChangeRequest() {
+  const adapter = inject(ChangeRequestAdapter);
+  return (data: Valid): Promise<Result<string, string>> =>
+    runSubmit(() => adapter.changeRequest(data), SUBMIT_FAILED);
+}
+```
+
+**Caller** (organism, field initializer — same shape as `createStore`): on the
+machine's `Submitting` state, run the command, then dispatch
+`SubmitConfirmed` / `SubmitFailed { error }`. Never throw into the template.
+
+## Optimistic updates on shared state
+
+When a root store's view must reflect the write before the server confirms:
+`begin*` (flip pending) → `confirm*` (clear + `resource.reload()`) / `rollback*`
+(undo). See `src/app/registratie/application/big-profile.store.ts`.
+
+## Worked examples
+
+- `src/app/registratie/infrastructure/change-request.adapter.ts`
+- `src/app/registratie/application/submit-change-request.ts`
+- `src/app/registratie/application/draft-sync.ts` — `createDraftSync(...)` bundles
+  draft persistence + submit for wizard flows; prefer it when the form has a draft.
+- `src/app/shared/application/submit.ts` — `runSubmit`, `SUBMIT_FAILED`.
+
+## Verify
+
+```bash
+npm test && npm run lint && npm run build
+# exercise the failure path in the browser: ?scenario=error on the submitting page
+```