docs(spec): frontend SPA milestone 1 (foundation slice) design

Decomposes the admin SPA into milestones; specs M1 — web/ scaffold,
Vite+React+TS+pnpm+shadcn/ui, openapi-typescript+openapi-fetch typed
client, TanStack Query, react-i18next (sv/en), two-pane master-detail
layout, login/session guard, read-only Objects browse, Vitest+RTL+MSW
tests, memory-serve embed behind a feature gate, 150KB bundle budget.

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

.gitignore

@@ -1,2 +1,4 @@
 /target
 .env
+
+.superpowers/